Make a system of equations.
\(\sf0.10d+0.25q=6\)
\(\sf~q = 2d\)
Plug in 2d for 'q' in the first equation:
\(\sf0.10d+0.25q=6\)
\(\sf0.10d+0.25(2d)=6\)
Multiply:
\(\sf0.10d+0.50d=6\)
Combine like terms:
\(\sf0.60d=6\)
Divide 0.60 to both sides:
\(\sf~d=10\)
Now plug this into any of the two equations to find 'q':
\(\sf~q = 2d\)
\(\sf~q = 2(10)\)
\(\sf~q = 20\)
So she has 10 dimes and 20 quarters.
