Question

Difficulty: MediumSystems of Linear Inequalities in Two Variables

A sports store orders standard helmets for 2020 dollars each and premium helmets for 5050 dollars each. The store can spend at most 22002{}200 dollars on this order. The distributor requires the store to order at least 6060 helmets in total. If the store decides to order at least 1515 premium helmets, what is the maximum number of standard helmets that the store can order?

Answer: 72 helmets

Answer

The maximum number of standard helmets the store can order is 72.
By setting the number of premium helmets to its minimum allowed value of 1515 to maximize the budget remaining for standard helmets, we find 20x≤145020x \leq 1450, which yields x≤72.5x \leq 72.5. Since standard helmets must be ordered in whole numbers, the maximum number is 7272, which also satisfies the minimum total order of 6060 helmets (72+15=87≥6072 + 15 = 87 \geq 60).

Step-by-Step Solution

1
Define variables and translate constraints into inequalities
Let xx be the number of standard helmets and yy be the number of premium helmets. The constraints are 20x+50y≤220020x + 50y \leq 2200, x+y≥60x + y \geq 60, and y≥15y \geq 15.
To represent the problem's mathematical relationships using a system of linear inequalities.
2
Solve for the upper limit of xx using the budget constraint and the minimum value of yy
Since 20x≤2200−50y20x \leq 2200 - 50y, xx is maximized when yy is at its minimum value, y=15y = 15. Substituting y=15y = 15 yields 20x+750≤2200  ⟹  20x≤1450  ⟹  x≤72.520x + 750 \leq 2200 \implies 20x \leq 1450 \implies x \leq 72.5.
To find the maximum possible value of standard helmets under the budget constraint.
3
Verify with the minimum total order constraint and determine the maximum integer value
Checking x+y≥60x + y \geq 60 with y=15y = 15 gives x+15≥60  ⟹  x≥45x + 15 \geq 60 \implies x \geq 45. Since xx must satisfy 45≤x≤72.545 \leq x \leq 72.5 and must be an integer, the maximum integer value is 7272.
To ensure the solution is physically possible as a whole number of items and satisfies all constraints.

Key Concept

Systems of Linear Inequalities in Two Variables
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