What's the equation for this?

Question

Supposed that the cost C, in dollars, of producing x chairs is given by C = 2x^2 - 40x + 2400. How many chairs can be produced for $4650?

Answer 1

4650 = 2x^2 - 40x + 2400
2x^2 - 40x - 2250 = 0
(2x - 90) (x + 25 ) = 0
2x = 90; x = 45 45 chairs
x = -25 Nope

Answer 2

Let C = $4650 = 2x^2 - 40x + 2400.

Then 0 = 2x² - 40x + (2400 - 4650) = 2x² - 40x - 2250.

Divide through by 2 to get the equation in lowest terms:

0 = x² - 20x - 1125.

Factor the right side, and set their product equal to 0:

(x + 25)(x - 45) = 0.

Now set each factor equal to 0 and solve for x:

x + 25 = 0 ---> x = -25.
x - 45 = 0 ---> x = 45.

Since the first result is negative, we reject it since we can't have negative numbers of chairs produced.

So the number of chairs which can be produced for $4650 is 45. To check your answer, simply plug it into the equation to see whether it makes it true. If it does, you are finished.

Answer 3

C = 2x^2 - 40x + 2400.
By the question. C = 4650. So:

2x^2 - 40x + 2400 =4650 or
2x^2 - 40x - 2250 = 0
So x = (1/4)(40 + ou - sq rt(1600+18000))
= (1/4)(40 + ou - 140)
= 45 or -25
- sign is not acceptable. So the number of chairs produced is 45. Answer.

Answer 4

U set cost=4650 and solve the quadratic equation.

Answer 5

uhhh....
4650 = 2x^2 -40 x + 2400
and then you find x
I do believe.... thats it