At the end of October, Gem had thrice as many 10-cent coins as 50-cent coins in her piggy bank. She took out 100 10-cent coins and exchanged it for 50-cent coins of the same value. In November, she saved another 15 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 November?
| |
10-cent |
50-cent |
Total |
| Before |
3 u |
1 u |
|
| Change 1 |
- 100 |
+ 20 |
|
| Change 2 |
+ 15 |
+ ? |
|
| 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 - 15 + 100
= 165
3 u = 165
1 u = 165 ÷ 3 = 55
Number of 50-cent coins in the end
= 4 p
= 4 x 80
= 320
Total value of 100 10-cent coins
= 100 x 10
= 1000¢
Number of 50-cent coins that was exchanged from 100 10-cent coins
= 1000 ÷ 50
= 20
Number of 50-cent coins that Gem saved in November
= 4 p - 1 u - 20
= 320 - 55 - 20
= 245
Answer(s): 245
