Question

50 POINTS!!! Word problem.

A class contributed $8.40 in dimes and quarters to the Red Cross. In all, there was 45 coins. How many coins of each kind were there?
Please also give an explanation. 50 points are a big deal.

Answer 1

Explanation:

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

Answer 2

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