Question

Timmy has almost $2.00 in allowance money that he wants to spend on candy. he has two favorite candies, one selling at $0.15 a piece and one at $0.08 a piece. if he ends up spending $1.92 on 17 pieces of candy, how many $0.15 pieces of candy did timmy decide to buy?

Answer 1

Let's call
 x = Amount of candy sold at $ 0.15.
 y = Amount of candy sold at $ 0.08.
 We must make the following system of equations:
 x + y = 17
 0.15x + 0.08y = 1.92
 Solving the system of equations:
 0.15x + 0.08 (17-x) = 1.92
 0.15x-0.08x + 1.36 = 1.92
 0.15x-0.08x = 1.92-1.36
 0.07x = 0.56
 x = 0.56 / 0.07 = 8
 On the other hand,
 x + y = 17
 8 + y = 17
 y = 17-8 = 9
 Finally, Timmy bought 8 pieces of candy for $ 0.15.