If y varies directly as x, and y = 20 when x = 4, what is the value of y when x = 10? — JAMB UTME

If $y$ varies directly as $x$ , and $y = 20$ when $x = 4$ , what is the value of $y$ when $x = 10$ ?

The value of

y

when

x = 10

is 50.

Direct variation means

y = kx

. Substituting

y = 20

and

x = 4

yields

k = 5

. Substituting

k = 5

and

x = 10

gives

y = 50

Set up the equation for direct variation

y = kx

, where

k

is the constant of variation.

Direct variation implies that

y

is directly proportional to

x

Substitute the given initial values (

y = 20

x = 4

) to find

k

20 = k(4) \implies k = \frac{20}{4} = 5

Determining the constant of variation allows us to write the specific relationship equation.

Calculate

y

when

x = 10

using the constant

k = 5

y = 5 \times 10 = 50

Substituting

x = 10

into

y = 5x

yields the required value.

Direct Variation (

y = kx

)

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