Albert had 3 coins and Ian had 10 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 19 coins. How many twenty-cent coins did they have at first?
|
Twenty-cent coins |
Fifty-cent coins |
Total |
Before |
19 - 5 u |
2 u |
13 |
Change |
+ 5 u |
- 2 u |
+ 3 u |
After |
19 |
0 |
19 |
Number of coins at first
= 3 + 10
= 13
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 = 19 - 13
3 u = 6
1 u = 6 ÷ 3 = 2
Number of twenty-cent coins at first
= 19 - 5 u
= 19 - 5 x 2
= 19 - 10
= 9
Answer(s): 9