11 – nickles and dimes, 0-10 dimes

17 – quarters, nickles and dimes, 8+6+3

11 – half dollars, 1+1+3+6

39 <== finally. i’ll get it, really i will.

the way to think about it is,

with only nickles and dimes, you can have 0, 1, 2, … 8, 10 dimes and the rest nickles

with quarters, you can have 4 or 3 or 2 or 1. if you have 3, then you can have 0, 1, 2 dimes. if you have 2 quarters, you can have 0, 1, 2, 3, 4, 5 dimes (and the rest nickles).

11 – nickles and dimes, 0-10 dimes

17 – quarters, nickles and dimes, 8+6+3

11 – half dollars, 1+1+3+6

39 <== finally. i’ll get it, really i will.

the way to think about it is,

with only nickles and dimes, you can have 0, 1, 2, … 8, 10 dimes and the rest nickles

with quarters, you can have 4 or 3 or 2 or 1. if you have 3, then you can have 0, 1, 2 dimes. if you have 2 quarters, you can have 0, 1, 2, 3, 4, 5 dimes (and the rest nickles).

References :