A class contributed $8.40 in dimes and quarters to the Red Cross. In all, there were 45 coins. How many coins of each kind were there?

Let d = # of dimes

Let q = # of quarters

45 = d + q

.1d +.25q = 8.40

Then we can use the substitution method and make it so that d = 45 - q.

Then plug in the value for d into the second equation.

.1 (45-q) +.25 (q) = 8.40

4.5-.1q+.25q=8.40

4.5+.15q = 8.40

.15q = 3.90

q = 26

d = 45 - 26 = 19

26 quarters

19 dimes