Question 880722
Hints:


You have 30 coins, so {{{n+d = 30}}}. You can solve for d to get {{{d = 30-n}}}


The coins total in value of $2.50, so {{{0.05n+0.10d=2.50}}}


You can then plug in {{{d = 30-n}}} to get {{{0.05n+0.10(30-n)=2.50}}}


Solving for n gives you the number of nickels. Use that to find the number of dimes.