A parking machine contained $3.05 made up of dimes and quarters. there were 20 coins in all. how many dimes were there?
1 dime = $0.10
1 quarter = $0.25
If we have x dimes, then we have (20-x) quarters.
x*0.1 + (20-x)*0.25 = 3.05
0.1x + 5 - 0.25x = 3.05
0.25x - 0.1x = 5 - 3.05
0.15x = 1.95
x = 1.95/0.15
x = 13 - number of dimes