The ratio of the number of green marbles to red marbles is 5 : 3. After Fred gives away 50 green marbles and buys another 70 red marbles, there is equal number of green marbles and red marbles. How many marbles does Fred have now?
| |
Green |
Red |
| Before |
5 u |
3 u |
| Change |
- 50 |
+ 70 |
| After |
5 u - 50 |
3 u + 70 |
The number of green marbles and red marbles in the end is the same.
5 u - 50 = 3 u + 70
5 u - 3 u = 70 + 50
2 u = 120
1 u = 120 ÷ 2 = 60
Number of marbles that Fred has now
= 5 u - 50 + 3 u + 70
= 5 u + 3 u - 50 + 70
= 8 u + 20
= 8 x 60 + 20
= 480 + 20
= 500
Answer(s): 500
