The ratio of the number of red cards to green cards is 3 : 1. After John gives away 80 red cards and buys another 90 green cards, there is equal number of red cards and green cards. How many cards does John have now?
| |
Red |
Green |
| Before |
3 u |
1 u |
| Change |
- 80 |
+ 90 |
| After |
3 u - 80 |
1 u + 90 |
The number of red cards and green cards in the end is the same.
3 u - 80 = 1 u + 90
3 u - 1 u = 90 + 80
2 u = 170
1 u = 170 ÷ 2 = 85
Number of cards that John has now
= 3 u - 80 + 1 u + 90
= 3 u + 1 u - 80 + 90
= 4 u + 10
= 4 x 85 + 10
= 340 + 10
= 350
Answer(s): 350
