Question 53427
{{{system(n+d+q=12, 5n + 10d + 25q = 100)}}}

{{{n+d+q = 12}}}
{{{n = 12-d-q}}}

{{{5(12-d-q) + 10d + 25q = 100}}}
{{{60 + 5d + 20q = 100}}}
{{{5d + 20q = 40}}}

You might have, by increasing number of quarters:

8 dimes, 4 nickels
4 dimes, 1 quarter and 7 nickels
2 quarters and 10 nickels

So it seems your solution is correct.