At the end of January, Sabrina had thrice as many 10-cent coins as 50-cent coins in her piggy bank. She took out 95 10-cent coins and exchanged it for 50-cent coins of the same value. In February, she saved another 20 10-cent coins and some 50-cent coins. She then had twice as many 50-cent coins in the end. She had 90 coins in the end. How many 50-cent coins did she save in February?
|
10-cent |
50-cent |
Total |
Before |
3 u |
1 u |
|
Change 1 |
- 95 |
+ 19 |
|
Change 2 |
+ 20 |
+ ? |
|
After |
1 p |
2 p |
90 |
Total number of coins in the end
= 1 p + 2 p
= 3 p
3 p = 90
1 p = 90 ÷ 3 = 30
Number of 10-cent in the end
= 1 p
= 30
Number of 10-cent at first
= 30 - 20 + 95
= 105
3 u = 105
1 u = 105 ÷ 3 = 35
Number of 50-cent coins in the end
= 2 p
= 2 x 30
= 60
Total value of 95 10-cent coins
= 95 x 10
= 950¢
Number of 50-cent coins that was exchanged from 95 10-cent coins
= 950 ÷ 50
= 19
Number of 50-cent coins that Sabrina saved in February
= 2 p - 1 u - 19
= 60 - 35 - 19
= 6
Answer(s): 6