Ian had 8 coins and Tom had 8 coins. Their coins consisted of ten-cent coins and twenty-cent coins. When all their twenty-cent coins were exchanged for ten-cent coins, they had a total of 19 coins. How many ten-cent coins did they have at first?
|
Ten-cent coins |
Twenty-cent coins |
Total |
Before |
19 - 2 u |
1 u |
16 |
Change |
+ 2 u |
- 1 u |
+ 1 u |
After |
19 |
0 |
19 |
Number of coins at first
= 8 + 8
= 16
1 twenty-cent coin can be exchanged for 2 ten-cent coins.
Increase in the number of coins after all the twenty-cent coins were exchanged for ten-cent coins
= 2 u - 1 u
= 1 u
1 u = 19 - 16 = 3
Number of ten-cent coins at first
= 19 - 2 u
= 19 - 2 x 3
= 19 - 6
= 13
Answer(s): 13