At the end of May, Shannon had twice as many 10-cent coins as 20-cent coins in her piggy bank. She took out 90 10-cent coins and exchanged it for 20-cent coins of the same value. In June, she saved another 64 10-cent coins and some 20-cent coins. She then had thrice as many 20-cent coins in the end. She had 280 coins in the end. How many 20-cent coins did she save in June?
| |
10-cent |
20-cent |
Total |
| Before |
2 u |
1 u |
|
| Change 1 |
- 90 |
+ 45 |
|
| Change 2 |
+ 64 |
+ ? |
|
| After |
1 p |
3 p |
280 |
Total number of coins in the end
= 1 p + 3 p
= 4 p
4 p = 280
1 p = 280 ÷ 4 = 70
Number of 10-cent in the end
= 1 p
= 70
Number of 10-cent at first
= 70 - 64 + 90
= 96
2 u = 96
1 u = 96 ÷ 2 = 48
Number of 20-cent coins in the end
= 3 p
= 3 x 70
= 210
Total value of 90 10-cent coins
= 90 x 10
= 900¢
Number of 20-cent coins that was exchanged from 90 10-cent coins
= 900 ÷ 20
= 45
Number of 20-cent coins that Shannon saved in June
= 3 p - 1 u - 45
= 210 - 48 - 45
= 117
Answer(s): 117
