The ratio of the number of blue marbles to green marbles is 7 : 2. After Charlie gives away 40 blue marbles and buys another 50 green marbles, there is equal number of blue marbles and green marbles. How many marbles does Charlie have now?
| |
Blue |
Green |
| Before |
7 u |
2 u |
| Change |
- 40 |
+ 50 |
| After |
7 u - 40 |
2 u + 50 |
The number of blue marbles and green marbles in the end is the same.
7 u - 40 = 2 u + 50
7 u - 2 u = 50 + 40
5 u = 90
1 u = 90 ÷ 5 = 18
Number of marbles that Charlie has now
= 7 u - 40 + 2 u + 50
= 7 u + 2 u - 40 + 50
= 9 u + 10
= 9 x 18 + 10
= 162 + 10
= 172
Answer(s): 172
