<PRE><B>Question 1116968</B>
A bookstore can purchase several calculators for a total cost of $160.
 If each calculator cost $4 less, the bookstore could purchase 2 additional calculators at the same total cost.
 How many calculators can be purchased at the regular price?
:
let c = no. of calc purchased at regular price
then
{{{160/c}}} = original price per calc
:
{{{160/c}}} - 4 = {{{160/((c+2))}}}
multiply by c(c+2), cancel denominators
160(c+2) - 4c(c+2) = 160c 
160c + 320 - 4c^2 - 8c = 160c
subtract 160c to both sides
320 - 4c^2 - 8c = 0
0 = 4c^2 + 8c - 320
simplify, divide by 4
c^2 + 2c - 80 = 0
factors to
(c+10)(c-8) = 0
positive solution
c = 8 calculators at regular price</PRE>