Question

tony had 13 bills in his wallet. they were all fives or tens. the total amount of money in his wallet was $90. How many five dollar bills did he have in his wallet?

Answer 1

//I'll let x = $5, y = $10
x + y = 13
5x + 10y = 90

So, y = 13 - x
5x + 10(13 - x) = 90
5x + 130 - 10x = 90
-5x = -40
x = 8