At the end of August, Min had four times as many 10-cent coins as 50-cent coins in her piggy bank. She took out 90 10-cent coins and exchanged it for 50-cent coins of the same value. In September, she saved another 6 10-cent coins and some 50-cent coins. She then had four times as many 50-cent coins in the end. She had 400 coins in the end. How many 50-cent coins did she save in September?
|
10-cent |
50-cent |
Total |
Before |
4 u |
1 u |
|
Change 1 |
- 90 |
+ 18 |
|
Change 2 |
+ 6 |
+ ? |
|
After |
1 p |
4 p |
400 |
Total number of coins in the end
= 1 p + 4 p
= 5 p
5 p = 400
1 p = 400 ÷ 5 = 80
Number of 10-cent in the end
= 1 p
= 80
Number of 10-cent at first
= 80 - 6 + 90
= 164
4 u = 164
1 u = 164 ÷ 4 = 41
Number of 50-cent coins in the end
= 4 p
= 4 x 80
= 320
Total value of 90 10-cent coins
= 90 x 10
= 900¢
Number of 50-cent coins that was exchanged from 90 10-cent coins
= 900 ÷ 50
= 18
Number of 50-cent coins that Min saved in September
= 4 p - 1 u - 18
= 320 - 41 - 18
= 261
Answer(s): 261