problem solving: Gina has saved $9.90 in dimes and quarters.

I am making these harder than I need to. I am mixing something up and can't seem to figure out where I am going wrong.

Gina has saved $9.90 in dimes and quarters. She has twice as many dimes as quarters. How many of each coin does Gina have?

Q=2d

.10d + .25q = 9.90

.10d + .25 (2d) = 9.90

.10d + .5d = 9.90
.6d=9.90
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9.90/.6=16.50=(d)

Q= 2 (16.50) = 33

I think "twice as many dimes as quarters" means "the number of dimes is twice the number of quarters", not the other way 'round.

Eliz.