Question 1171320
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The only constraint on the numbers of hats and t-shirts is the amount of money they have to spend buying the items.  Common sense -- or a basic familiarity with the formal method of solving this kind of problem -- tells us that the maximum profit is either with only hats or with only t-shirts.<br>
For $2250, the maximum number of hats they can buy is 2250/5 = 450; by selling 450 shirts their profit would be 450*$4 = $1800.<br>
For $2250, the maximum number of t-shirts they can buy is 2250/9 = 250; by selling 250 t-shirts their profit would be 250*$5 =$1250.<br>
ANSWER: the maximum profit is obtained by buy and sell only 450 hats.<br>