The value of all the quarters and dimes in a parking meter is $18. There are twice as many quarters

The value of all the quarters and dimes in a parking meter is $18. There are twice as many quarters as dimes. What is the total number of dimes in the parking meter?

Let q be the number of quarters. Let d be the number of dimes. We're given:

1. q = 2d
2. 0.10d + 0.25q = 18

Substitute (1) into (2):
0.10d + 0.25(2d) = 18
0.10d + 0.5d = 18

Type this equation into our search engine, and we get d = 30.