tower records charges $15.49 per CD. Online, you can get CDs for $13.99 each, plus $6 shipping. Find the # of CDs that you can by for the same amount at the 2 stores

Answer 1

15.49X = 13.99X + 6

15.49-13.99X = 6

1.50X = 6

X = 6/1.50 = 4

Buy 4 and the price is the same at both stores.

Buy less than 4 and it's cheaper at Tower Records

Buy more than 4 and it's cheaper on line

In economics terms, the variable cost is $15.49 at Towers with fixed cost = 0

variable cost on line is $13.99 and fixed cost $6

You could graph these cost functions, and get straight lines that intersect at x=4, total cost = $61.96

Towers graph is a straight line from the origin with larger slope than the slope of the online straight line

Answer 2

Let x be the number of CDs bought. Then we have the following equation:

13.99x + 6 = 15.49x

Isolate the variables. Subtract 13.99x on both sides to get:

1.50x = 6

Divide both sides by 1.50 to get x = 4.

You can buy 4 CDs for the same amount from the 2 stores.