Answer: 10 dimes
Solve using system of equations.
q=number of quarters and d=number of dimes
.25q+.10d=5.50 because the total of dimes and quarters is $5.50
8+d=q because there are 8 more quarters than dimes
substitute 8+d for q into the first equation to get .25(8+d)+.10d=5.50
then simplify
2+.35d=5.50
.35d=3.50
d=10 he has 10 dimes