SOLUTION: When a popular brand of CD player is priced at $320 per unit, a store sells 12 units per week. Each time the price is reduced by $11, however, the sales increase by 2 per week. Wha

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Question 123651This question is from textbook algebra and trigonometry with analiytic geometry
: When a popular brand of CD player is priced at $320 per unit, a store sells 12 units per week. Each time the price is reduced by $11, however, the sales increase by 2 per week. What selling price will result in weekly revenues of $5166?
Please enter your answer as a number without the units.
This question is from textbook algebra and trigonometry with analiytic geometry

Answer by edjones(8007) About Me  (Show Source):
You can put this solution on YOUR website!
price * # of units = revenues.
Let x= # of price reductions
(320-11x)*(12+2x)=5166
-22x^2+508x+3840=5166
-22x^2+508x-1326=0
-11x^2+254x-663=0
x=3, x=20.091
320-11*3= $287. Ans.
.
Check:
(320-11*3)*(12+2*3)
=287*18
=5166
.
The other answer is also correct but the number of price reductions is not even.
The sales price would be $99.
.
Ed
Solved by pluggable solver: SOLVE quadratic equation (work shown, graph etc)
Quadratic equation ax%5E2%2Bbx%2Bc=0 (in our case -11x%5E2%2B254x%2B-663+=+0) has the following solutons:

x%5B12%5D+=+%28b%2B-sqrt%28+b%5E2-4ac+%29%29%2F2%5Ca

For these solutions to exist, the discriminant b%5E2-4ac should not be a negative number.

First, we need to compute the discriminant b%5E2-4ac: b%5E2-4ac=%28254%29%5E2-4%2A-11%2A-663=35344.

Discriminant d=35344 is greater than zero. That means that there are two solutions: +x%5B12%5D+=+%28-254%2B-sqrt%28+35344+%29%29%2F2%5Ca.

x%5B1%5D+=+%28-%28254%29%2Bsqrt%28+35344+%29%29%2F2%5C-11+=+3
x%5B2%5D+=+%28-%28254%29-sqrt%28+35344+%29%29%2F2%5C-11+=+20.0909090909091

Quadratic expression -11x%5E2%2B254x%2B-663 can be factored:
-11x%5E2%2B254x%2B-663+=+%28x-3%29%2A%28x-20.0909090909091%29
Again, the answer is: 3, 20.0909090909091. Here's your graph:
graph%28+500%2C+500%2C+-10%2C+10%2C+-20%2C+20%2C+-11%2Ax%5E2%2B254%2Ax%2B-663+%29