Tommy had 8 coins and Justin had 12 coins. Their coins consisted of twenty-cent coins and fifty-cent coins. When all their fifty-cent coins were exchanged for twenty-cent coins, they had a total of 35 coins. How many twenty-cent coins did they have at first?
| |
Twenty-cent coins |
Fifty-cent coins |
Total |
| Before |
35 - 5 u |
2 u |
20 |
| Change |
+ 5 u |
- 2 u |
+ 3 u |
| After |
35 |
0 |
35 |
Number of coins at first
= 8 + 12
= 20
2 fifty-cent coins can be exchanged for 5 twenty-cent coins.
Increase in the number of coins after all the fifty-cent coins were exchanged for twenty-cent coins
= 5 u - 2 u
= 3 u
3 u = 35 - 20
3 u = 15
1 u = 15 ÷ 3 = 5
Number of twenty-cent coins at first
= 35 - 5 u
= 35 - 5 x 5
= 35 - 25
= 10
Answer(s): 10
