Let d = # of dimes
Let q = # of quarters
equation #1: number of coins
d + q = 1234
equation #2: value of coins
0.10d + 0.25q = 290.05
Solve #1 for d:
d=1234-q
Sub #1 into #2 and solve for q:
0.10d + 0.25q = 290.05
0.10(1234-q) + 0.25q = 290.05
123.4 - 0.10q + 0.25q = 290.05
0.15q = 166.65
q = 1111
Now go back to d=1234-q and sub in 1111 for q to find d:
d = 1234 - 1111
d = 123
1111 quarters and 123 dimes.
