Answer:
25 dimes
Explanation:
Given
Coins: Nickels (N), Quarters (Q) , and Dimes (D)
$0.05 = 1 nickel, $0.10 = 1 dime and $0.25 = 1 quarter
So, the amount implies:

The number of coin implies:

and
Required
Determine the number of Dimes


Substitute 7 + Q for N in the first and second equation



Collect Like Terms

----- (1)


Collect Like Terms


Make Q the subject



Substitute 20.5 - 0.50D for Q in (1)






Solve for D


Hence, there are 25 Dimes