
a. Let us say that c(x) is the cost of one t shirt based on the number of increases therefore:
c = 10 + x
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b. Say that t(x) is the number of t shirts sold based on the number of increases so:
 t = 2500 – 100 x
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b. The revenue is simply the product:
r(x) = (10 + x) (2500 – 100 x)
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Combining:
r(x) = 25000 – 1000 x + 2500 x – 100 x^2
r(x) = 25000 + 1500 x – 100 x^2
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Taking the 1st derivative and setting dr / dx = 0 to get the maxima:
dr / dx = 1500 – 200 x
1500 = 200 x
x = 7.5
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t = 2500 – 100 x = 2500 – 100 (7.5) = 1750
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Hence 1750 shirts should be sold.
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