Luis had 10 coins and John had 10 coins. Their coins consisted of ten-cent coins and fifty-cent coins. When all their fifty-cent coins were exchanged for ten-cent coins, they had a total of 36 coins. How many ten-cent coins did they have at first?
| |
Ten-cent coins |
Fifty-cent coins |
Total |
| Before |
36 - 5 u |
1 u |
20 |
| Change |
+ 5 u |
- 1 u |
+ 4 u |
| After |
36 |
0 |
36 |
Number of coins at first
= 10 + 10
= 20
1 fifty-cent coin can be exchanged for 5 ten-cent coins.
Increase in the number of coins after all the fifty-cent coins were exchanged for ten-cent coins
= 5 u - 1 u
= 4 u
4 u = 36 - 20
4 u = 16
1 u = 16 ÷ 4 = 4
Number of ten-cent coins at first
= 36 - 5 u
= 36 - 5 x 4
= 36 - 20
= 16
Answer(s): 16
