At the end of July, Roshel had thrice as many 20-cent coins as 50-cent coins in her piggy bank. She took out 75 20-cent coins and exchanged it for 50-cent coins of the same value. In August, she saved another 46 20-cent coins and some 50-cent coins. She then had twice as many 50-cent coins in the end. She had 210 coins in the end. How many 50-cent coins did she save in August?
|
20-cent |
50-cent |
Total |
Before |
3 u |
1 u |
|
Change 1 |
- 75 |
+ 30 |
|
Change 2 |
+ 46 |
+ ? |
|
After |
1 p |
2 p |
210 |
Total number of coins in the end
= 1 p + 2 p
= 3 p
3 p = 210
1 p = 210 ÷ 3 = 70
Number of 20-cent in the end
= 1 p
= 70
Number of 20-cent at first
= 70 - 46 + 75
= 99
3 u = 99
1 u = 99 ÷ 3 = 33
Number of 50-cent coins in the end
= 2 p
= 2 x 70
= 140
Total value of 75 20-cent coins
= 75 x 20
= 1500¢
Number of 50-cent coins that was exchanged from 75 20-cent coins
= 1500 ÷ 50
= 30
Number of 50-cent coins that Roshel saved in August
= 2 p - 1 u - 30
= 140 - 33 - 30
= 77
Answer(s): 77