Calculus homework, please help.

Calculus
Tutor: None Selected Time limit: 1 Day

  1. The marginal profit in dollars on Brie cheese sold at a cheese store is given by P'(x) = x(90x^2 + 30x), where x is the amount of cheese sold, in hundreds of pounds. The "profit" is -$60 when no cheese is sold. a) Find the profit function, and b) Find the profit from selling 400 pounds of Brie cheese.
May 7th, 2015

a). P'(x) = x(90x^2 + 30x)

when x=0 / profit=-$60 the profit function is

P'(x) = 90x^3 + 30x^2 -$60

b). when x=400

P'(x) = 90(400)^3 + 30(400)^2 -$60

=$5764799940



May 7th, 2015

I can't access part b yet, but when I entered the answer you provided for part a, it was incorrect, for whatever reason. It's asking for P(x) = 

May 7th, 2015

do you have any question about what i have done

May 7th, 2015

ok let me integrate

May 7th, 2015
P'(x) = 90x^3 + 30x^2
p(x)=(90/4)x^4 +(30/3)x^3-60
p(x)=22.5x^4 +10x^3 -60
is this correct??


May 7th, 2015

Yes, that was correct. So then B will be different, correct? Thank you so much for doing the work. :) I'll leave a good rating.

May 7th, 2015

b). p(x)=22.5x^4 +10x^3 -60

x=400

p(x)=22.5(400)^4 +10(400)^3 -60

=$5.7664

May 7th, 2015

That was incorrect, and now the whole problem has to be redone. :( 

The new problem reads as follows: The marginal profit in dollars on Brie cheese sold at a cheese store is given by P'(x) = x(20x^2 + 30x), where x is the amount of cheese sold, in hundreds of pounds. The "profit" is -$70 when no cheese is sold. a) Find the profit function, and b) Find the profit from selling 200 pounds of Brie cheese.

May 7th, 2015

If it's easier, could you possibly do these (or in addition to)? 

  1. Find the cost function if the marginal cost function is given by C'(x) = x^(2/5) + 9
  2. Find the demand function for the marginal revenue function. Recall that if no items are sold, the revenue is R'(x) = .03x^2 - .07x + 208

May 7th, 2015

Never mind those, I'm working on them. But I do need the initial one. :/ I apologize.

May 7th, 2015
Find the profit from selling 200 pounds of Brie cheese.

b) Find the profit from selling 400 pounds of Brie cheese.

which of these was i to do??? i had these answers for the 400.which of them is correct

$5764799940 and $5.7664

May 7th, 2015

Neither of them were, actually. When I tried those and one variation, it gave me a new problem after three wrong answers. Now it's the one I re-wrote above. I should have taken note of the answer it gave.

May 7th, 2015

was i supposed to use 400 or 200??

May 7th, 2015

For the initial question, as I first posted it, it was 400 pounds, but with the program we must use for homework, we are given three tries until it gives us a similar example to try to solve. Hence why both parts a and b need to be re-worked.

May 7th, 2015

but you told me part (a) was correct

May 7th, 2015

It was for the first form of the question, but since part b was not, it reset the entire question; they were two parts of the same submission. 

It's okay if you don't want to do it again... I understand.

May 7th, 2015

no you don,t understand, part b involves substitution for the value of x, and part a was correct, i don't know why part b is wrong

May 7th, 2015

I do understand why you're questioning it. I saw the methodology and worked it out to the same conclusion. However, the final answer they had was six-thousand-something.

May 7th, 2015

ok then, i wish i was able to understand it much better. i also saw the 2nd question but since i did not get the first one correct, i decided not to take it. i feel happy when i deliver the best answers and satisfy my students

May 7th, 2015

That's okay... I understand. Best regards and thanks for the work you did.

May 7th, 2015

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