The ratio of the number of red marbles to blue marbles is 9 : 2. After Ian gives away 20 red marbles and buys another 50 blue marbles, there is equal number of red marbles and blue marbles. How many marbles does Ian have now?
| |
Red |
Blue |
| Before |
9 u |
2 u |
| Change |
- 20 |
+ 50 |
| After |
9 u - 20 |
2 u + 50 |
The number of red marbles and blue marbles in the end is the same.
9 u - 20 = 2 u + 50
9 u - 2 u = 50 + 20
7 u = 70
1 u = 70 ÷ 7 = 10
Number of marbles that Ian has now
= 9 u - 20 + 2 u + 50
= 9 u + 2 u - 20 + 50
= 11 u + 30
= 11 x 10 + 30
= 110 + 30
= 140
Answer(s): 140
