At the end of May, Penelope had thrice as many 10-cent coins as 50-cent coins in her piggy bank. She took out 60 10-cent coins and exchanged it for 50-cent coins of the same value. In June, she saved another 61 10-cent coins and some 50-cent coins. She then had twice as many 50-cent coins in the end. She had 300 coins in the end. How many 50-cent coins did she save in June?
| |
10-cent |
50-cent |
Total |
| Before |
3 u |
1 u |
|
| Change 1 |
- 60 |
+ 12 |
|
| Change 2 |
+ 61 |
+ ? |
|
| After |
1 p |
2 p |
300 |
Total number of coins in the end
= 1 p + 2 p
= 3 p
3 p = 300
1 p = 300 ÷ 3 = 100
Number of 10-cent in the end
= 1 p
= 100
Number of 10-cent at first
= 100 - 61 + 60
= 99
3 u = 99
1 u = 99 ÷ 3 = 33
Number of 50-cent coins in the end
= 2 p
= 2 x 100
= 200
Total value of 60 10-cent coins
= 60 x 10
= 600¢
Number of 50-cent coins that was exchanged from 60 10-cent coins
= 600 ÷ 50
= 12
Number of 50-cent coins that Penelope saved in June
= 2 p - 1 u - 12
= 200 - 33 - 12
= 155
Answer(s): 155
