At the end of June, Fanny had thrice as many 20-cent coins as 50-cent coins in her piggy bank. She took out 100 20-cent coins and exchanged it for 50-cent coins of the same value. In July, she saved another 10 20-cent coins and some 50-cent coins. She then had thrice as many 50-cent coins in the end. She had 240 coins in the end. How many 50-cent coins did she save in July?
|
20-cent |
50-cent |
Total |
Before |
3 u |
1 u |
|
Change 1 |
- 100 |
+ 40 |
|
Change 2 |
+ 10 |
+ ? |
|
After |
1 p |
3 p |
240 |
Total number of coins in the end
= 1 p + 3 p
= 4 p
4 p = 240
1 p = 240 ÷ 4 = 60
Number of 20-cent in the end
= 1 p
= 60
Number of 20-cent at first
= 60 - 10 + 100
= 150
3 u = 150
1 u = 150 ÷ 3 = 50
Number of 50-cent coins in the end
= 3 p
= 3 x 60
= 180
Total value of 100 20-cent coins
= 100 x 20
= 2000¢
Number of 50-cent coins that was exchanged from 100 20-cent coins
= 2000 ÷ 50
= 40
Number of 50-cent coins that Fanny saved in July
= 3 p - 1 u - 40
= 180 - 50 - 40
= 90
Answer(s): 90