The ratio of the number of green marbles to red marbles is 7 : 5. After Ken gives away 70 green marbles and buys another 80 red marbles, there is equal number of green marbles and red marbles. How many marbles does Ken have now?
| |
Green |
Red |
| Before |
7 u |
5 u |
| Change |
- 70 |
+ 80 |
| After |
7 u - 70 |
5 u + 80 |
The number of green marbles and red marbles in the end is the same.
7 u - 70 = 5 u + 80
7 u - 5 u = 80 + 70
2 u = 150
1 u = 150 ÷ 2 = 75
Number of marbles that Ken has now
= 7 u - 70 + 5 u + 80
= 7 u + 5 u - 70 + 80
= 12 u + 10
= 12 x 75 + 10
= 900 + 10
= 910
Answer(s): 910
