A purse contains 15 coins worth $1.35. If there are only dimes and nickels in the purse, how many coins of each kind are there?

informally this problem only requires a working knowledge of counting money
12 dimes: $1.20
3 nickels:$0.15
buck thirty five!

formally:
coins: n+d=15
cash value: 0.05n+0.10d=$1.35 (which we multiply by 20 for convenience)
n+2d=27
then
(n+2d)-(n+d)=27-15

d=12
so n=3



:)