The ratio of the number of green cards to red cards is 7 : 5. After Charlie gives away 10 green cards and buys another 50 red cards, there is equal number of green cards and red cards. How many cards does Charlie have now?
| |
Green |
Red |
| Before |
7 u |
5 u |
| Change |
- 10 |
+ 50 |
| After |
7 u - 10 |
5 u + 50 |
The number of green cards and red cards in the end is the same.
7 u - 10 = 5 u + 50
7 u - 5 u = 50 + 10
2 u = 60
1 u = 60 ÷ 2 = 30
Number of cards that Charlie has now
= 7 u - 10 + 5 u + 50
= 7 u + 5 u - 10 + 50
= 12 u + 40
= 12 x 30 + 40
= 360 + 40
= 400
Answer(s): 400
