At the end of January, Gwen had twice as many 10-cent coins as 20-cent coins in her piggy bank. She took out 50 10-cent coins and exchanged it for 20-cent coins of the same value. In February, she saved another 42 10-cent coins and some 20-cent coins. She then had thrice as many 20-cent coins in the end. She had 360 coins in the end. How many 20-cent coins did she save in February?
| |
10-cent |
20-cent |
Total |
| Before |
2 u |
1 u |
|
| Change 1 |
- 50 |
+ 25 |
|
| Change 2 |
+ 42 |
+ ? |
|
| After |
1 p |
3 p |
360 |
Total number of coins in the end
= 1 p + 3 p
= 4 p
4 p = 360
1 p = 360 ÷ 4 = 90
Number of 10-cent in the end
= 1 p
= 90
Number of 10-cent at first
= 90 - 42 + 50
= 98
2 u = 98
1 u = 98 ÷ 2 = 49
Number of 20-cent coins in the end
= 3 p
= 3 x 90
= 270
Total value of 50 10-cent coins
= 50 x 10
= 500¢
Number of 20-cent coins that was exchanged from 50 10-cent coins
= 500 ÷ 20
= 25
Number of 20-cent coins that Gwen saved in February
= 3 p - 1 u - 25
= 270 - 49 - 25
= 196
Answer(s): 196
