Question

Joseph sold tickets to the school musical. He had 12 bills worth $175 for the ticketssold. If all the money was $5 bills, $10 bills, and $20 bills, how many of each bill did he have?

Answer 1

if he had x,y,z bills of $5,$10,$20 respectively,

x+y+z = 12
5x+10y+20z = 175

A third equation would help, so we have to do some trial and error.

1 $5
5 $10
6 $20