At the end of October, Kimberly had twice as many 10-cent coins as 50-cent coins in her piggy bank. She took out 65 10-cent coins and exchanged it for 50-cent coins of the same value. In November, she saved another 77 10-cent coins and some 50-cent coins. She then had twice as many 50-cent coins in the end. She had 270 coins in the end. How many 50-cent coins did she save in November?
|
10-cent |
50-cent |
Total |
Before |
2 u |
1 u |
|
Change 1 |
- 65 |
+ 13 |
|
Change 2 |
+ 77 |
+ ? |
|
After |
1 p |
2 p |
270 |
Total number of coins in the end
= 1 p + 2 p
= 3 p
3 p = 270
1 p = 270 ÷ 3 = 90
Number of 10-cent in the end
= 1 p
= 90
Number of 10-cent at first
= 90 - 77 + 65
= 78
2 u = 78
1 u = 78 ÷ 2 = 39
Number of 50-cent coins in the end
= 2 p
= 2 x 90
= 180
Total value of 65 10-cent coins
= 65 x 10
= 650¢
Number of 50-cent coins that was exchanged from 65 10-cent coins
= 650 ÷ 50
= 13
Number of 50-cent coins that Kimberly saved in November
= 2 p - 1 u - 13
= 180 - 39 - 13
= 128
Answer(s): 128