Let
x = the number of dimes
y = the number of quarters
The total sum is $2.05, therefore
0.10x + 0.25y = 2.05
Divide through by 0.05 to obtain
2x + 5y = 41 (1)
There are 3 fewer quarters than dimes, therefore
y = x - 3 (2)
Substitute (2) into (1).
2x + 5(x - 3) = 41
2x + 5x - 15 = 41
7x = 56
x = 8
y = x - 3 = 5
Answer: 8 dimes, 5 quarters
