Oliver had 8 coins and Neave had 3 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 17 coins. How many twenty-cent coins did they have at first?
| |
Twenty-cent coins |
Fifty-cent coins |
Total |
| Before |
17 - 5 u |
2 u |
11 |
| Change |
+ 5 u |
- 2 u |
+ 3 u |
| After |
17 |
0 |
17 |
Number of coins at first
= 8 + 3
= 11
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 = 17 - 11
3 u = 6
1 u = 6 ÷ 3 = 2
Number of twenty-cent coins at first
= 17 - 5 u
= 17 - 5 x 2
= 17 - 10
= 7
Answer(s): 7
