Theory of Consumer Behaviour

93 questions

All types93 Multiple choice53 True / False13 Numeric17 Matching8 Short answer2

Why does a standard indifference curve slope downward from left to right?

To obtain additional units of one commodity, the consumer must give up some units of another commodity to maintain the same level of satisfaction.

The marginal rate of substitution between the two commodities remains strictly constant along the curve.

Total utility drops to zero at the point where one commodity is substituted for another.

The total financial expenditure required to purchase the commodity combination increases continuously.

Show answer & explanation

Answer: To obtain additional units of one commodity, the consumer must give up some units of another commodity to maintain the same level of satisfaction.

Answer

A standard indifference curve slopes downward from left to right because to obtain additional units of one commodity, the consumer must give up some units of another commodity to maintain the same level of overall satisfaction.

A standard indifference curve has a negative slope (downward from left to right) because both goods yield positive utility. If a consumer consumes more of one commodity, they must reduce their consumption of the other commodity so that total utility remains unchanged.

Step-by-Step Solution

Recall the definition of an indifference curve.

An indifference curve shows all combinations of two goods that give a consumer equal total satisfaction.

Knowing that satisfaction is constant along the curve is necessary to determine its slope.

Analyze the utility impact of increasing one good.

Consuming more of Good X increases satisfaction.

Both goods are assumed to have positive marginal utility (more is preferred to less).

Determine the required compensation in the other good.

To keep total satisfaction constant, consumption of Good Y must decrease, yielding a negative (downward) slope.

A gain in utility from one good must be offset by a loss in utility from the other good.

Key Concept

Negative Slope of Indifference Curves

Question 62Question →

A consumer experiences a fall in the price of Good Y. As a result, the substitution effect causes the consumer to buy 8 additional units of Good Y, while the income effect leads the consumer to buy 3 fewer units of Good Y. What is the net total price effect on the quantity demanded of Good Y, and how is Good Y classified?

An increase of 5 units; Good Y is an inferior good

An increase of 11 units; Good Y is a normal good

A decrease of 5 units; Good Y is a Giffen good

An increase of 8 units; Good Y is a normal good

Show answer & explanation

Answer: An increase of 5 units; Good Y is an inferior good

Answer

An increase of 5 units in quantity demanded, classifying Good Y as an inferior good.

The total price effect is calculated by adding the substitution effect and the income effect:

+8 + (-3) = +5

units. Because a fall in price increases real income, and this higher real income causes the consumer to reduce consumption of Good Y by 3 units, Good Y is an inferior good. However, since the positive substitution effect (+8) exceeds the negative income effect (-3), the overall quantity demanded increases by 5 units.

Step-by-Step Solution

Calculate the total price effect

Total Effect = Substitution Effect + Income Effect = (+8) + (-3) = +5 units

The total price effect on demand is the algebraic sum of the substitution effect and the income effect.

Determine the direction of the income effect relative to the price change

A fall in price increases real purchasing power, but the income effect leads to buying 3 fewer units.

When an increase in real income leads to a decrease in consumption, the good is by definition an inferior good.

Compare the magnitudes of substitution and income effects

Substitution effect (+8) > Income effect (-3), so net quantity demanded increases (+5).

Since the substitution effect outweighs the negative income effect, the law of demand still holds, distinguishing a non-Giffen inferior good from a Giffen good.

Key Concept

Decomposition of Price Effect into Substitution and Income Effects for Inferior Goods

Estimated Time:2m 0s

Question 63Question →

An individual consumes two commodities, $X$ and $Y$ , with market prices $P_x = \text{₦}150$ and $P_y = \text{₦}50$ respectively. At a given point $K$ on their budget constraint, the marginal rate of substitution of $X$ for $Y$ ( $MRS_{xy}$ ) equals $3$ . Why is the condition $MRS_{xy} = \frac{P_x}{P_y}$ at point $K$ alone NOT sufficient to guarantee a stable consumer equilibrium under ordinal utility theory?

Tangency must be supported by the strict convexity of the indifference curve to the origin at point

K

to satisfy the second-order condition for utility maximization.

The marginal utility of money spent on Good

X

must equal zero at point

K

to confirm total satisfaction.

The slope of the indifference curve must remain constant along the entire length of the budget line.

The consumer must allocate equal monetary expenditure to Good

X

and Good

Y

at point

K

Show answer & explanation

Answer: Tangency must be supported by the strict convexity of the indifference curve to the origin at point $K$ to satisfy the second-order condition for utility maximization.

Answer

The condition of tangency (

MRS_{xy} = \frac{P_x}{P_y}

) must be fulfilled alongside the second-order condition that the indifference curve is strictly convex to the origin at the point of contact.

In ordinal utility theory, consumer equilibrium requires two conditions to be satisfied: (1) First-order necessary condition:

MRS_{xy} = \frac{P_x}{P_y}

(tangency of the budget line and indifference curve), and (2) Second-order sufficient condition: the indifference curve must be strictly convex to the origin at the tangency point. Convexity ensures diminishing

MRS_{xy}

, guaranteeing that utility is maximized rather than minimized.

Step-by-Step Solution

Calculate the price ratio of Good

X

to Good

Y

\frac{P_x}{P_y} = \frac{150}{50} = 3

The slope of the budget line is given by the relative price ratio of the two commodities.

Compare the marginal rate of substitution (

MRS_{xy}

) to the price ratio

MRS_{xy} = 3 = \frac{P_x}{P_y}

This establishes that the necessary (first-order) condition for consumer equilibrium is met at point

K

Evaluate the second-order condition required for stable equilibrium

The indifference curve must be convex to the origin (diminishing

MRS_{xy}

If the indifference curve were concave or linear at the point of tangency, the consumer would minimize utility or achieve a corner solution rather than maximizing utility.

Key Concept

Consumer Equilibrium under Ordinal Utility (First-Order and Second-Order Conditions)

Estimated Time:2m 0s

Question 64Question →

If a consumer's total money income and the price of Good $X$ (plotted on the horizontal axis) both double while the price of Good $Y$ (plotted on the vertical axis) remains constant, the horizontal intercept of the budget line remains unchanged while the line becomes steeper.

True

False

Show answer & explanation

Answer: True

Answer

The statement is TRUE.

The horizontal intercept

\frac{I}{P_X}

remains unchanged because both money income (

I

) and the price of Good

X

(

P_X

) increase by the same proportion (doubling). The absolute slope of the budget line

\frac{P_X}{P_Y}

doubles because

P_X

doubles while

P_Y

stays constant, causing the budget line to pivot upward along the vertical axis to

\frac{2I}{P_Y}

and become steeper.

Step-by-Step Solution

Determine the initial horizontal intercept and slope of the budget line.

The initial horizontal intercept is

\frac{I}{P_X}

and the absolute slope is

\frac{P_X}{P_Y}

This establishes the baseline affordability boundary for Good

X

and the relative price ratio.

Calculate the new horizontal intercept after income (

I

) and the price of Good

X

(

P_X

) double.

The new horizontal intercept is

\frac{2I}{2P_X} = \frac{I}{P_X}

Proportionate increases in money income and the price of a good cancel each other out in the horizontal intercept calculation.

Calculate the new absolute slope of the budget line after

P_X

doubles while

P_Y

remains unchanged.

The new absolute slope is

\frac{2P_X}{P_Y}

, which is twice as steep as the original slope

\frac{P_X}{P_Y}

Good

X

has become twice as expensive relative to Good

Y

, requiring the consumer to give up more units of Good

Y

for each additional unit of Good

X

Key Concept

Effects of non-proportionate price and income changes on budget line intercepts and slope

Estimated Time:1m 15s

Question 65Question →

A consumer is indifferent among five bundles of Commodity $X$ and Commodity $Y$ as presented in the schedule below:

Combination	Commodity $X$ (units)	Commodity $Y$ (units)
P	1	16
Q	2	11
R	3	7
S	4	4
T	5	2

Based on this schedule, what is the Marginal Rate of Substitution of $X$ for $Y$ ( $MRS_{xy}$ ) when the consumer moves from combination R to combination S, and what fundamental geometric property of the indifference curve does the overall trend of $MRS_{xy}$ demonstrate?

3 units of

Y

for 1 unit of

X

; diminishing

MRS_{xy}

resulting in convexity to the origin

4 units of

Y

for 1 unit of

X

; constant

MRS_{xy}

resulting in a linear downward slope

3 units of

Y

for 1 unit of

X

; total utility falling to zero at the point of maximum consumption

7 units of

Y

for 1 unit of

X

; increasing

MRS_{xy}

resulting in concavity to the origin

Show answer & explanation

Answer: 3 units of $Y$ for 1 unit of $X$ ; diminishing $MRS_{xy}$ resulting in convexity to the origin

Answer

The Marginal Rate of Substitution of

X

for

Y

from combination R to S is 3 units of

Y

per unit of

X

, and the overall pattern demonstrates a diminishing

MRS_{xy}

, which explains why indifference curves are convex to the origin.

The change in good

Y

given up when moving from bundle R (3X, 7Y) to bundle S (4X, 4Y) is

7 - 4 = 3

units of

Y

for 1 unit of

X

. Furthermore, evaluating the whole schedule shows that the

MRS_{xy}

steadily declines (

5 \rightarrow 4 \rightarrow 3 \rightarrow 2

), which directly explains the fundamental property of standard indifference curves being convex to the origin.

Step-by-Step Solution

Calculate the Marginal Rate of Substitution (

MRS_{xy}

) when moving from combination R to combination S.

MRS_{xy} = \frac{-\Delta Y}{\Delta X} = \frac{7 - 4}{4 - 3} = \frac{3}{1} = 3

units of

Y

per unit of

X

MRS measure the quantity of good

Y

a consumer is willing to give up to gain one additional unit of good

X

while maintaining the same level of utility.

Analyze the trend of

MRS_{xy}

across all successive consumption bundles in the schedule.

From P to Q:

MRS = 5

; Q to R:

MRS = 4

; R to S:

MRS = 3

; S to T:

MRS = 2

As consumption of

X

increases, the consumer values additional units of

X

relatively less in terms of

Y

Relate the diminishing trend of

MRS_{xy}

to the corresponding property of the indifference curve.

The diminishing

MRS_{xy}

gives rise to an indifference curve that is convex to the origin.

Because the slope of the curve (

-\frac{dY}{dX} = MRS_{xy}

) decreases in magnitude as

X

increases, the curve flattens out toward the right, forming a convex shape.

Key Concept

Indifference Curve Convexity and Diminishing Marginal Rate of Substitution (MRS)

Estimated Time:2m 0s

Question 66Question →

A consumer allocating a fixed income between Good $X$ and Good $Y$ faces market prices of $P_x = \text{₦}60$ and $P_y = \text{₦}15$ . At their current consumption bundle, the Marginal Rate of Substitution ( $MRS_{xy}$ ) is $3$ . Assuming standard indifference curves that are strictly convex to the origin, how should the consumer adjust their purchases to attain equilibrium?

Decrease consumption of Good

X

and increase consumption of Good

Y

Increase consumption of Good

X

and decrease consumption of Good

Y

Increase consumption of both Good

X

and Good

Y

simultaneously

Maintain the current consumption bundle without modification

Show answer & explanation

Answer: Decrease consumption of Good $X$ and increase consumption of Good $Y$

Answer

The consumer should decrease consumption of Good

X

and increase consumption of Good

Y

In ordinal utility analysis, consumer equilibrium is reached at the point where the indifference curve is tangent to the budget line, satisfying the condition

MRS_{xy} = \frac{P_x}{P_y}

. Given

P_x = \text{₦}60

and

P_y = \text{₦}15

, the market price ratio is

\frac{60}{15} = 4

. Since the current

MRS_{xy}

3

, which is less than

4

, the consumer values Good

X

less than the market does at the margin. To raise

MRS_{xy}

to match the market ratio of

4

, the consumer must decrease consumption of Good

X

and increase consumption of Good

Y

along the budget constraint.

Step-by-Step Solution

Calculate the market price ratio of Good

X

to Good

Y

\frac{P_x}{P_y} = \frac{60}{15} = 4.

The price ratio determines the slope of the budget line.

Compare the current Marginal Rate of Substitution (

MRS_{xy}

) to the price ratio.

MRS_{xy} = 3 < \frac{P_x}{P_y} = 4.

Equilibrium under ordinal utility requires

MRS_{xy} = \frac{P_x}{P_y}

at the point of tangency.

Determine the necessary adjustment to restore equilibrium along a convex indifference curve.

Reduce Good

X

and increase Good

Y

to increase

MRS_{xy}

from

3

4

Due to the diminishing rate of marginal substitution, reducing consumption of

X

increases

MU_x

and increasing consumption of

Y

decreases

MU_y

, which raises

MRS_{xy} = \frac{MU_x}{MU_y}

toward

4

Key Concept

Consumer Equilibrium under Ordinal Utility

Estimated Time:2m 0s

Question 67Question →

In ordinal utility analysis, a rational consumer maximizes satisfaction subject to a budget constraint at the point of tangency between an indifference curve and the budget line. At this equilibrium point, the Marginal Rate of Substitution ( $MRS_{xy}$ ) must be equal to which of the following?

The price ratio of the two commodities (

\frac{P_x}{P_y}

)

The ratio of the total utilities of the two commodities (

\frac{TU_x}{TU_y}

)

A constant slope along a straight-line indifference curve

The combined sum of the market prices (

P_x + P_y

)

Show answer & explanation

Answer: The price ratio of the two commodities ( $\frac{P_x}{P_y}$ )

Answer

The price ratio of the two commodities (

\frac{P_x}{P_y}

)

In ordinal utility theory, consumer equilibrium is achieved when the consumer maximizes utility given their budget constraint. Graphically, this happens at the point where the highest attainable indifference curve is tangent to the budget line, meaning the slope of the indifference curve (

MRS_{xy}

) equals the price ratio of the two goods (

\frac{P_x}{P_y}

Step-by-Step Solution

Identify the graphical condition for consumer equilibrium in ordinal utility theory.

Equilibrium occurs at the point of tangency between the budget line and the highest reachable indifference curve.

At the point of tangency, the slope of the indifference curve matches the slope of the budget line.

Equate the mathematical definitions for the slopes.

The slope of the indifference curve is

MRS_{xy}

and the slope of the budget line is

\frac{P_x}{P_y}

, yielding

MRS_{xy} = \frac{P_x}{P_y}

This condition ensures the rate at which the consumer is willing to trade good

X

for good

Y

equals the rate at which the market allows them to trade.

Key Concept

Consumer Equilibrium under Ordinal Utility

Question 68Question →

When the price of Good X increases, the substitution effect causes a consumer to decrease their consumption of Good X by $7$ units. If the net total price effect results in an overall increase of $3$ units in the quantity demanded of Good X, which of the following correctly classifies Good X and describes the direction and magnitude of the income effect?

Good X is a Giffen good, and the income effect causes an increase of

10

units in quantity demanded.

Good X is a standard inferior good, and the income effect causes a decrease of

10

units in quantity demanded.

Good X is a Giffen good, and the income effect causes an increase of

4

units in quantity demanded.

Good X is a normal good, and the income effect causes an increase of

3

units in quantity demanded.

Show answer & explanation

Answer: Good X is a Giffen good, and the income effect causes an increase of $10$ units in quantity demanded.

Answer

Good X is a Giffen good, and the income effect causes an increase of

10

units in quantity demanded.

The total price effect is the algebraic sum of the substitution effect and the income effect (

TE = SE + IE

). When the price of a commodity rises, the substitution effect is strictly negative (

-7

units). To achieve an overall increase in quantity demanded of

+3

units, the income effect must equal

+10

units. Because the income effect acts in the opposite direction of the substitution effect and is powerful enough to outweigh it, the commodity is definitively classified as a Giffen good.

Step-by-Step Solution

Set up the fundamental decomposition formula for price effect

Total Effect (

TE

) = Substitution Effect (

SE

) + Income Effect (

IE

)

According to ordinal utility theory, the total price effect on quantity demanded is decomposed into substitution and income components.

Calculate the magnitude and direction of the income effect

+3 = -7 + IE \implies IE = +10

units

A price increase always produces a negative substitution effect (

SE = -7

). For the overall quantity demanded to increase by

3

units (

TE = +3

), the income effect must be

+10

units.

Determine the economic classification of the good

Good X is a Giffen good

A Giffen good is an extreme case of an inferior good where the positive income effect from a price increase is stronger than the negative substitution effect, resulting in a positively sloped demand curve.

Key Concept

Decomposition of Price Effect into Income and Substitution Effects for Giffen Goods

Question 69Question →

A consumer allocates household income between cassava flour and yam. Cassava flour is classified as an inferior good, but not a Giffen good. If the market price of cassava flour increases, which of the following correctly describes the directional impacts of the substitution effect and the income effect on the quantity of cassava flour demanded?

The substitution effect reduces quantity demanded, while the income effect increases quantity demanded, resulting in an overall net decrease in quantity demanded.

Both the substitution effect and the income effect reduce quantity demanded, reinforcing an overall net decrease in quantity demanded.

The substitution effect increases quantity demanded, while the income effect reduces quantity demanded, leading to an overall net increase in quantity demanded.

The substitution effect reduces quantity demanded, but the income effect increases quantity demanded by a greater magnitude, resulting in an overall net increase in quantity demanded.

Show answer & explanation

Answer: The substitution effect reduces quantity demanded, while the income effect increases quantity demanded, resulting in an overall net decrease in quantity demanded.

Answer

The substitution effect reduces quantity demanded, while the income effect increases quantity demanded, resulting in an overall net decrease in quantity demanded.

When the price of a good increases, the substitution effect always causes a decrease in quantity demanded as consumers shift toward relatively cheaper alternatives. For an inferior good, a rise in price lowers real income, which leads consumers to purchase more of the inferior item (a positive income effect). Because the commodity is specified as a non-Giffen inferior good, the negative substitution effect is stronger than the positive income effect, causing the net total price effect to be negative (overall decrease in quantity demanded).

Step-by-Step Solution

Analyze the direction of the substitution effect following a price increase.

The substitution effect is always negative relative to price changes. An increase in price makes cassava flour relatively more expensive than yam, prompting the consumer to substitute away from cassava flour (reducing quantity demanded).

The substitution effect measures movement along an indifference curve due to relative price changes alone.

Analyze the direction of the income effect for an inferior good following a price increase.

A price increase reduces real purchasing power. Because cassava flour is an inferior good, a decline in real income leads the consumer to demand more of it (positive income effect).

Inferior goods have an inverse relationship between real income and quantity demanded.

Compare the relative magnitudes of the substitution effect and income effect for a standard (non-Giffen) inferior good.

For a non-Giffen inferior good,

|\text{Substitution Effect}| > |\text{Income Effect}|

. Thus, the reduction from substitution exceeds the increase from the income effect, yielding a net decrease in total quantity demanded.

A Giffen good requires the income effect to exceed the substitution effect; since this good is non-Giffen, the law of demand still holds.

Key Concept

Decomposition of Total Price Effect for Inferior Goods

Estimated Time:2m 0s

Question 70Question →

If the price of an inferior commodity (which is not a Giffen good) decreases, how do the substitution effect and the income effect interact to influence the quantity demanded of the commodity?

The substitution effect increases quantity demanded, while the income effect reduces quantity demanded, but the substitution effect is stronger.

Both the substitution effect and the income effect operate in the same direction to increase the quantity demanded.

The substitution effect reduces quantity demanded, while the income effect increases quantity demanded, resulting in no overall change.

The income effect reduces quantity demanded by a greater amount than the substitution effect increases it, causing total quantity demanded to fall.

Show answer & explanation

Answer: The substitution effect increases quantity demanded, while the income effect reduces quantity demanded, but the substitution effect is stronger.

Answer

The substitution effect increases quantity demanded, while the income effect reduces quantity demanded, but the substitution effect is stronger.

When the price of an inferior commodity falls, it becomes relatively cheaper, causing consumers to substitute toward it (positive substitution effect). However, the price drop increases purchasing power (real income), which causes consumers to buy less of an inferior good (negative income effect). Because it is not a Giffen good, the substitution effect dominates the income effect, leading to a net increase in quantity demanded.

Step-by-Step Solution

Analyze the substitution effect of a price reduction

A lower price makes the good relatively cheaper compared to substitutes, so the substitution effect always increases quantity demanded of the good.

The substitution effect is strictly negative with respect to price (moving in the opposite direction of price change).

Analyze the income effect of a price reduction for an inferior good

A price reduction increases real income. For an inferior good, an increase in real income leads to a decrease in quantity demanded.

By definition of inferior goods, demand moves inversely with real income.

Determine the net total price effect for a non-Giffen inferior good

The total price effect remains positive (overall quantity demanded increases) because the substitution effect outweighs the income effect.

For standard inferior goods, the positive substitution effect is larger in magnitude than the opposing negative income effect.

Key Concept

Decomposition of Price Effect for Inferior Goods

Question 71Question →

A consumer's maximum willingness to pay for four successive bags of rice is ₦15,000, ₦13,000, ₦11,000, and ₦9,000 respectively. If the prevailing market price per bag is ₦9,000, what is the total consumer surplus derived in Naira?

Show answer & explanation

Answer: 12000

Answer

The total consumer surplus derived by the consumer is ₦12,000.

Consumer surplus is the difference between total willingness to pay and total actual expenditure. The total willingness to pay for the 4 bags of rice is ₦15,000 + ₦13,000 + ₦11,000 + ₦9,000 = ₦48,000. Since each bag costs ₦9,000, total expenditure for 4 bags is 4 × ₦9,000 = ₦36,000. Subtracting ₦36,000 from ₦48,000 gives a consumer surplus of ₦12,000.

Step-by-Step Solution

Sum the maximum willingness to pay for all consumed units to find Total Willingness to Pay.

Total Willingness to Pay = ₦15,000 + ₦13,000 + ₦11,000 + ₦9,000 = ₦48,000.

Total utility or willingness to pay is the cumulative value derived from consuming all 4 units.

Multiply the number of purchased units by the market price per unit to calculate Total Actual Expenditure.

Total Expenditure = 4 × ₦9,000 = ₦36,000.

The market price applies uniformly to all units purchased.

Subtract Total Expenditure from Total Willingness to Pay to calculate Consumer Surplus.

Consumer Surplus = ₦48,000 - ₦36,000 = ₦12,000.

Consumer surplus is defined as the net benefit (Total Willingness to Pay minus Total Expenditure).

Key Concept

Concept and Calculation of Consumer Surplus

Alternative Method

Alternatively, calculate the individual surplus for each unit (Willingness to Pay - Market Price) and sum them up: 1st unit (₦15,000 - ₦9,000 = ₦6,000), 2nd unit (₦13,000 - ₦9,000 = ₦4,000), 3rd unit (₦11,000 - ₦9,000 = ₦2,000), 4th unit (₦9,000 - ₦9,000 = ₦0). Total Consumer Surplus = ₦6,000 + ₦4,000 + ₦2,000 + ₦0 = ₦12,000.

Estimated Time:1m 0s

Question 72Question →

A consumer's preferences for Commodity $A$ and Commodity $B$ are illustrated on an indifference map containing multiple indifference curves. When the consumer transitions from a consumption bundle on Indifference Curve $IC_1$ to a bundle on Indifference Curve $IC_2$ located further to the northeast, which of the following best explains why $IC_2$ represents a higher level of satisfaction?

The higher curve contains consumption bundles with larger quantities of at least one good without reducing the quantity of the other.

The marginal rate of substitution remains constant along all points on the higher curve.

The total utility on the lower curve drops to zero as the consumer moves to the right.

The two indifference curves will eventually intersect at the consumer equilibrium point.

Show answer & explanation

Answer: The higher curve contains consumption bundles with larger quantities of at least one good without reducing the quantity of the other.

Answer

The higher curve contains consumption bundles with larger quantities of at least one good without reducing the quantity of the other.

Under standard ordinal utility theory and the assumption of non-satiation (monotonic preferences), consumers prefer more goods to fewer goods. An indifference curve located higher and further to the northeast of another contains bundles with strictly greater quantities of at least one good without reducing the quantity of the other good, thus providing a strictly higher level of total satisfaction.

Step-by-Step Solution

Recall the fundamental properties of an indifference map.

Indifference curves positioned further to the right or northeast represent higher levels of utility.

Economic theory assumes monotonic preferences (more of a good is preferred to less).

Analyze what moving northeast on a two-good graph implies geometrically.

Moving northeast means increasing the amount of Commodity

A

, Commodity

B

, or both.

Higher quantities of normal goods yield higher total utility.

Evaluate the offered explanations against indifference curve properties.

The correct explanation directly links position to bundle composition and non-satiation.

The assumption that consumer preferences are non-satiated means larger bundles provide greater utility.

Key Concept

Indifference Map and Utility Levels

Question 73Question →

A consumer's evaluation of total utility derived from consuming successive tubers of yam in a local Nigerian market (expressed in monetary terms) is presented in the table below:

Quantity of Yam (Tubers)	Total Utility (₦)
1	1,800
2	3,300
3	4,500
4	5,400
5	6,000
6	6,300

If the prevailing market price of a tuber of yam is ₦900, what is the total value of consumer surplus (in ₦) enjoyed by the consumer at equilibrium?

Show answer & explanation

Answer: 1800

Answer

The consumer surplus enjoyed by the consumer at equilibrium is ₦1,800.

To find consumer surplus, one must first establish the consumer's profit-maximizing equilibrium quantity where Marginal Utility (MU) equals Price (P). From the Total Utility (TU) values, the MU for successive units is ₦1,800, ₦1,500, ₦1,200, and ₦900. At the 4th unit, MU equals the market price of ₦900. Total utility for 4 units is ₦5,400 and total outlay is

4 \times 900 = \text{₦}3,600

. Subtracting total outlay from total utility yields a consumer surplus of ₦1,800.

Step-by-Step Solution

Calculate Marginal Utility (MU) for each unit consumed

MU values are ₦1,800 for the 1st tuber, ₦1,500 for the 2nd, ₦1,200 for the 3rd, ₦900 for the 4th, ₦600 for the 5th, and ₦300 for the 6th tuber.

Consumer equilibrium is reached when the marginal utility of a unit equals its market price.

Determine the equilibrium quantity consumed

The consumer purchases 4 tubers of yam.

For the 4th tuber,

MU = \text{₦}900

, which matches the prevailing market price of ₦900. Consuming a 5th tuber yields

MU = \text{₦}600 < \text{₦}900

, which reduces net utility.

Calculate the actual total expenditure

\text{Total Expenditure} = 4 \times \text{₦}900 = \text{₦}3,600

Total expenditure is equal to the quantity purchased multiplied by the market price per unit.

Subtract Total Expenditure from Total Utility to find Consumer Surplus

\text{Consumer Surplus} = \text{₦}5,400 - \text{₦}3,600 = \text{₦}1,800

Consumer surplus measures the difference between total willingness to pay (Total Utility at 4 units) and actual expenditure.

Key Concept

Calculation of Consumer Surplus from Discrete Utility Schedules

Question 74Question →

When the price of a normal good decreases, the total increase in the quantity demanded by a consumer is driven by both the substitution effect and the income effect. Which statement correctly describes how these two effects operate in response to this price reduction?

Both the substitution effect and the income effect work in the same direction to increase the quantity demanded.

The substitution effect increases the quantity demanded, while the income effect reduces it.

The income effect increases the quantity demanded, while the substitution effect reduces it.

The substitution effect causes a movement along the demand curve, while the income effect shifts the demand curve outwards.

Show answer & explanation

Answer: Both the substitution effect and the income effect work in the same direction to increase the quantity demanded.

Answer

Both the substitution effect and the income effect reinforce each other in the same direction to increase the quantity demanded of a normal good when its price falls.

When the price of a normal good falls, two distinct phenomena occur: first, the good becomes relatively less expensive than substitute goods, prompting the consumer to substitute into it (substitution effect increases quantity demanded); second, the consumer's real purchasing power rises, and since it is a normal good, higher real purchasing power induces further consumption (income effect increases quantity demanded). Thus, both effects operate in tandem to raise total quantity demanded.

Step-by-Step Solution

Analyze the substitution effect of a price reduction.

As the good becomes relatively cheaper compared to other goods, the consumer substitutes toward this good, increasing quantity demanded.

The substitution effect is always negative with respect to price changes (moving in the opposite direction of price).

Analyze the income effect of a price reduction for a normal good.

A lower price increases the consumer's real income (purchasing power). Because the good is normal, higher real income leads to increased consumption of the good.

By definition, demand for a normal good moves in the same direction as changes in real income.

Combine the two effects to find the net total price effect.

Both effects reinforce each other, resulting in a net increase in total quantity demanded.

Total Price Effect = Substitution Effect + Income Effect.

Key Concept

Directional Alignment of Income and Substitution Effects for Normal Goods

Estimated Time:1m 0s

Question 75Question →

An economic study tracks a consumer's purchasing adjustment following an increase in the price of Good X. The findings are summarized in the table below:

Economic Effect	Change in Quantity Demanded
Substitution Effect	$-12$ units
Income Effect	$+15$ units

Based on the data provided, what type of good is Good X, and what is the net change in its total quantity demanded?

Good X is a Giffen good, and its total quantity demanded increases by

3

units.

Good X is a standard inferior good (non-Giffen), and its total quantity demanded decreases by

3

units.

Good X is a normal good, and its total quantity demanded increases by

27

units.

Good X is a normal good, and its total quantity demanded decreases by

15

units.

Show answer & explanation

Answer: Good X is a Giffen good, and its total quantity demanded increases by $3$ units.

Answer

Good X is a Giffen good, and its total quantity demanded increases by 3 units.

The Total Price Effect equation states that

\text{Total Effect} = \text{Substitution Effect} + \text{Income Effect}

. With a price increase, the substitution effect always induces a negative change in quantity demanded (

-12

units). A positive income effect (

+15

units) following a price increase (which lowers real income) identifies Good X as an inferior good. Because the magnitude of this positive income effect (

15

) exceeds the substitution effect (

12

), the total quantity demanded increases by

+3

units. An inferior good whose positive income effect outweighs the negative substitution effect is classified as a Giffen good.

Step-by-Step Solution

Calculate Total Price Effect

\text{Total Effect} = \text{Substitution Effect} + \text{Income Effect} = -12 + 15 = +3

units.

The total price effect on quantity demanded is the algebraic sum of the substitution effect and the income effect.

Determine Good Classification from Income Effect Direction

Good X is an inferior good.

When the price of a good increases, real income falls. A positive change in quantity demanded (

+15

units) resulting from reduced real income indicates an inferior good.

Evaluate Giffen Good Criteria

Good X is a Giffen good because

|\text{Income Effect}| > |\text{Substitution Effect}|

When the positive income effect of an inferior good outweighs the negative substitution effect, the total demand curve slopes upward with respect to price, satisfying the definition of a Giffen good.

Key Concept

Decomposition of Price Effect into Substitution and Income Effects for Giffen Goods

Estimated Time:2m 0s

Question 76Question →

If a consumer spends a fixed money income exclusively on Good $X$ (plotted on the horizontal axis) and Good $Y$ (plotted on the vertical axis), a simultaneous per-unit tax on Good $X$ and per-unit subsidy on Good $Y$ will cause the budget line to pivot inward along the horizontal axis, pivot outward along the vertical axis, and become steeper.

True

False

Show answer & explanation

Answer: True

Answer

The statement is True. Increasing the price of the horizontal good while decreasing the price of the vertical good reduces the horizontal intercept, expands the vertical intercept, and increases the magnitude of the slope (

P_X / P_Y

), making the budget line steeper.

The statement is correct because taxing Good

X

raises

P_X

while subsidizing Good

Y

lowers

P_Y

. The absolute slope of the budget line equals

P_X / P_Y

. A higher numerator (

P_X

) and a lower denominator (

P_Y

) increase the value of

P_X / P_Y

, resulting in a steeper budget line anchored to a smaller horizontal intercept and a larger vertical intercept.

Step-by-Step Solution

Analyze the impact on the horizontal intercept (

I / P_X

Taxing Good

X

increases

P_X

, which decreases

I / P_X

and pivots the horizontal intercept inward toward the origin.

The horizontal intercept represents total income divided by the price of Good

X

Analyze the impact on the vertical intercept (

I / P_Y

Subsidizing Good

Y

decreases

P_Y

, which increases

I / P_Y

and pivots the vertical intercept outward away from the origin.

The vertical intercept represents total income divided by the price of Good

Y

Determine the change in the budget line slope magnitude (

P_X / P_Y

With

P_X

rising and

P_Y

falling, the price ratio

P_X / P_Y

increases, causing the budget line to become steeper.

The slope of the budget line measures the rate at which Good

Y

must be given up for Good

X

in the market.

Key Concept

Budget Line Rotation and Slope Dynamics

Estimated Time:1m 15s

Question 77Question →

A household's maximum willingness to pay for successive kegs of palm oil is given in the table below:

Unit (Keg)	Maximum Willingness to Pay (₦)
1st	500
2nd	450
3rd	400
4th	350
5th	300

If the market price per keg is ₦350, what is the total consumer surplus derived by the household?

₦150

₦300

₦1,350

₦1,700

Show answer & explanation

Answer: ₦300

Answer

The total consumer surplus derived by the household is ₦300.

The correct answer is ₦300. At a market price of ₦350, the household consumes 4 kegs of palm oil because willingness to pay equals price at the 4th unit. Total willingness to pay for 4 kegs is ₦500 + ₦450 + ₦400 + ₦350 = ₦1,700. The actual expenditure is 4 × ₦350 = ₦1,400. Thus, consumer surplus = ₦1,700 - ₦1,400 = ₦300.

Step-by-Step Solution

Determine the quantity of palm oil kegs the household will purchase at the market price of ₦350.

The consumer will buy up to the 4th keg because for the 4th keg, willingness to pay (��350) equals market price (₦350). The 5th keg will not be purchased because willingness to pay (₦300) is less than market price.

A rational consumer purchases additional units as long as willingness to pay is greater than or equal to market price.

Calculate the total willingness to pay (total monetary utility) for the 4 purchased kegs.

Total Willingness to Pay = ₦500 + ₦450 + ₦400 + ₦350 = ₦1,700.

Total willingness to pay is the sum of maximum prices the consumer is prepared to pay for each consumed unit.

Calculate the actual total expenditure incurred by buying 4 kegs at ₦350 each.

Total Expenditure = 4 units × ₦350 = ₦1,400.

Actual expenditure is calculated as total quantity purchased multiplied by prevailing market price.

Subtract actual total expenditure from total willingness to pay to obtain consumer surplus.

Consumer Surplus = ₦1,700 - ₦1,400 = ₦300.

Consumer surplus measures the net economic benefit or gain derived by consumers when paying less than their maximum willingness to pay.

Key Concept

Consumer Surplus from Marginal Utility / Willingness to Pay Schedule

Question 78Question →

Which of the following theoretical reasons explains why standard indifference curves can never intersect each other?

Intersection violates the assumption of transitivity by implying that two distinct levels of total satisfaction yield equal utility.

Intersection causes the marginal rate of substitution between goods to remain constant along both curves.

Intersection forces total utility to reach its maximum point where marginal utility becomes zero.

Intersection implies that the consumer is unwilling to substitute one good for another at any point on the curves.

Show answer & explanation

Answer: Intersection violates the assumption of transitivity by implying that two distinct levels of total satisfaction yield equal utility.

Answer

Intersection violates the assumption of transitivity by implying that two distinct levels of total satisfaction yield equal utility.

Indifference curves cannot intersect because if they did, the point of intersection would belong to two different utility levels. By transitivity, all points on both curves would yield the exact same utility, which contradicts the concept that higher or distinct curves represent different satisfaction levels.

Step-by-Step Solution

Identify the core property being evaluated.

The property is the non-intersection of indifference curves.

Indifference curves represent combinations of two goods that give a consumer equal satisfaction.

Analyze the logical consequence if two curves (

IC_1

and

IC_2

) were to cross at a point (

A

Point

A

lies on both

IC_1

and

IC_2

If bundle

B

is on

IC_1

, then

A \sim B

. If bundle

C

is on

IC_2

, then

A \sim C

Apply the axiom of transitivity.

A \sim B

and

A \sim C

, then

B \sim C

Transitivity dictates that if bundle

A

gives equal satisfaction to

B

and

C

, then

B

and

C

must give equal satisfaction. However,

B

and

C

lie on distinct curves representing different overall utility levels, creating a logical contradiction.

Key Concept

Non-intersection property of indifference curves derived from preference transitivity

Estimated Time:1m 0s

Question 79Question →

For a Giffen good, when its price decreases, the positive substitution effect on quantity demanded is outweighed by a negative income effect, causing the total quantity demanded to decrease.

True

False

Show answer & explanation

Answer: True

Answer

The statement is true because for a Giffen good, the negative income effect resulting from a price fall is greater in magnitude than the positive substitution effect, leading to a net reduction in quantity demanded.

The statement accurately reflects the theoretical decomposition of the price effect for a Giffen good: a fall in price enhances real income, generating a negative income effect that exceeds the positive substitution effect, thereby reducing the net quantity demanded.

Step-by-Step Solution

Determine the direction of the substitution effect following a price drop.

The substitution effect is always positive when the price of a good falls, incentivizing consumers to buy more of that good relative to others.

Lower relative price drives substitution toward the cheaper commodity regardless of whether the good is normal or inferior.

Analyze the income effect of a price reduction for a Giffen good.

A drop in price increases real income. For a strongly inferior good (Giffen good), an increase in real income leads to a decrease in quantity demanded (negative income effect).

Inferior goods exhibit an inverse relationship between real income and quantity demanded.

Evaluate the net total price effect (

TE = SE + IE

For a Giffen good,

|IE| > |SE|

, causing the negative income effect to dominate the positive substitution effect, producing a net decrease in total quantity demanded.

The defining characteristic of a Giffen good is an income effect that overpowers the substitution effect, resulting in an upward-sloping demand curve.

Key Concept

Income and Substitution Effects on Giffen Goods

Question 80Question →

A consumer's evaluation of marginal utility (maximum willingness to pay) for purchasing successive bottles of fruit juice is presented in the table below:

Unit (Bottle)	Willingness to Pay (₦)
1st bottle	500
2nd bottle	400
3rd bottle	300
4th bottle	200
5th bottle	100

If the prevailing market price per bottle is ₦200, what is the total consumer surplus derived from consuming the optimal quantity of fruit juice?

₦300

₦600

₦1,200

₦1,400

Show answer & explanation

Answer: ₦600

Answer

The total consumer surplus derived is ₦600.

The correct option is ₦600 because the consumer will buy 4 bottles (where willingness to pay ≥ ₦200). Total willingness to pay is ₦500 + ₦400 + ₦300 + ₦200 = ₦1,400, while total outlay is 4 × ₦200 = ₦800. Net consumer surplus is ₦1,400 - ₦800 = ₦600.

Step-by-Step Solution

Determine the optimal quantity consumed.

4 bottles are purchased.

A rational consumer continues purchasing as long as Marginal Utility (willingness to pay) is greater than or equal to the market price (₦200). The 5th bottle is excluded because its willingness to pay (₦100) is below market price.

Calculate total willingness to pay (Total Utility in monetary terms) for the optimal quantity.

Total Willingness to Pay = ₦500 + ₦400 + ₦300 + ₦200 = ₦1,400.

Summing the consumer's maximum valuation for each of the 4 units purchased.

Calculate total expenditure paid by the consumer.

Total Expenditure = 4 units × ₦200 = ₦800.

Multiplying the quantity bought by the market price per unit.

Compute consumer surplus.

Consumer Surplus = ₦1,400 - ₦800 = ₦600.

Consumer surplus is the difference between total willingness to pay and total actual expenditure.

Key Concept

Consumer Surplus from Marginal Utility Schedule

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