At the end of October, Rachel had twice as many 10-cent coins as 50-cent coins in her piggy bank. She took out 70 10-cent coins and exchanged it for 50-cent coins of the same value. In November, she saved another 20 10-cent coins and some 50-cent coins. She then had four times as many 50-cent coins in the end. She had 200 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 |
- 70 |
+ 14 |
|
Change 2 |
+ 20 |
+ ? |
|
After |
1 p |
4 p |
200 |
Total number of coins in the end
= 1 p + 4 p
= 5 p
5 p = 200
1 p = 200 ÷ 5 = 40
Number of 10-cent in the end
= 1 p
= 40
Number of 10-cent at first
= 40 - 20 + 70
= 90
2 u = 90
1 u = 90 ÷ 2 = 45
Number of 50-cent coins in the end
= 4 p
= 4 x 40
= 160
Total value of 70 10-cent coins
= 70 x 10
= 700¢
Number of 50-cent coins that was exchanged from 70 10-cent coins
= 700 ÷ 50
= 14
Number of 50-cent coins that Rachel saved in November
= 4 p - 1 u - 14
= 160 - 45 - 14
= 101
Answer(s): 101