The ratio of the number of red marbles to blue marbles is 7 : 2. After Luke gives away 30 red marbles and buys another 90 blue marbles, there is equal number of red marbles and blue marbles. How many marbles does Luke have now?
| |
Red |
Blue |
| Before |
7 u |
2 u |
| Change |
- 30 |
+ 90 |
| After |
7 u - 30 |
2 u + 90 |
The number of red marbles and blue marbles in the end is the same.
7 u - 30 = 2 u + 90
7 u - 2 u = 90 + 30
5 u = 120
1 u = 120 ÷ 5 = 24
Number of marbles that Luke has now
= 7 u - 30 + 2 u + 90
= 7 u + 2 u - 30 + 90
= 9 u + 60
= 9 x 24 + 60
= 216 + 60
= 276
Answer(s): 276
