At the end of June, Ivory had thrice as many 10-cent coins as 20-cent coins in her piggy bank. She took out 100 10-cent coins and exchanged it for 20-cent coins of the same value. In July, she saved another 45 10-cent coins and some 20-cent coins. She then had twice as many 20-cent coins in the end. She had 240 coins in the end. How many 20-cent coins did she save in July?
| |
10-cent |
20-cent |
Total |
| Before |
3 u |
1 u |
|
| Change 1 |
- 100 |
+ 50 |
|
| Change 2 |
+ 45 |
+ ? |
|
| After |
1 p |
2 p |
240 |
Total number of coins in the end
= 1 p + 2 p
= 3 p
3 p = 240
1 p = 240 ÷ 3 = 80
Number of 10-cent in the end
= 1 p
= 80
Number of 10-cent at first
= 80 - 45 + 100
= 135
3 u = 135
1 u = 135 ÷ 3 = 45
Number of 20-cent coins in the end
= 2 p
= 2 x 80
= 160
Total value of 100 10-cent coins
= 100 x 10
= 1000¢
Number of 20-cent coins that was exchanged from 100 10-cent coins
= 1000 ÷ 20
= 50
Number of 20-cent coins that Ivory saved in July
= 2 p - 1 u - 50
= 160 - 45 - 50
= 65
Answer(s): 65
