Jack had 6 coins and Archie had 13 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 34 coins. How many twenty-cent coins did they have at first?
| |
Twenty-cent coins |
Fifty-cent coins |
Total |
| Before |
34 - 5 u |
2 u |
19 |
| Change |
+ 5 u |
- 2 u |
+ 3 u |
| After |
34 |
0 |
34 |
Number of coins at first
= 6 + 13
= 19
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 = 34 - 19
3 u = 15
1 u = 15 ÷ 3 = 5
Number of twenty-cent coins at first
= 34 - 5 u
= 34 - 5 x 5
= 34 - 25
= 9
Answer(s): 9
