The ratio of the number of green marbles to red marbles is 3 : 1. After Andy gives away 50 green marbles and buys another 90 red marbles, there is equal number of green marbles and red marbles. How many marbles does Andy have now?
| |
Green |
Red |
| Before |
3 u |
1 u |
| Change |
- 50 |
+ 90 |
| After |
3 u - 50 |
1 u + 90 |
The number of green marbles and red marbles in the end is the same.
3 u - 50 = 1 u + 90
3 u - 1 u = 90 + 50
2 u = 140
1 u = 140 ÷ 2 = 70
Number of marbles that Andy has now
= 3 u - 50 + 1 u + 90
= 3 u + 1 u - 50 + 90
= 4 u + 40
= 4 x 70 + 40
= 280 + 40
= 320
Answer(s): 320
