Originally Posted by

**craziebbygirl** The question is: A fast food restaurant determines the cost and revenue models for its hamburgers to be:

c = .06X = 7500 ; 0 <= X <= 50000

r= (1/20000)(65000x - x^2) ; 0 <= X <= 50000

a. Write the profit function for this situation

b. determine the intervals the function decreases / increases

c. determine how many hamburgers the restaurant needs to sell to obtain max profit.

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I have found the profit function to be p= r-c

so I got : P = (1/20000)(65000x - x^2) - (.6x + 7500)

and P'= (65000x - x^2) + (1/20000)(65000 - x) - .6

but this is not the answer in the book. I'm not sure what I am doing wrong.

Thanks!