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An electronics store purchases stereos from a supply company at a cost of each. They currently sell the stereos for each. At this price the store is averaging sales per week. Marketing studies show that for every decrease in price, the store will sell an additional five stereos. What price should the store use to maximize their profits?

Calculate the current revenue:
Profit: -
Number sold:

Adjust the current revenue equation:
Let the number of times the price is decreased by .

Optimize (that is, use derivatives to find the optimal value of ). But note, the question is asking about price, not .