The ratio of the number of red marbles to blue marbles is 7 : 3. After Oscar gives away 30 red marbles and buys another 50 blue marbles, there is equal number of red marbles and blue marbles. How many marbles does Oscar have now?
| |
Red |
Blue |
| Before |
7 u |
3 u |
| Change |
- 30 |
+ 50 |
| After |
7 u - 30 |
3 u + 50 |
The number of red marbles and blue marbles in the end is the same.
7 u - 30 = 3 u + 50
7 u - 3 u = 50 + 30
4 u = 80
1 u = 80 ÷ 4 = 20
Number of marbles that Oscar has now
= 7 u - 30 + 3 u + 50
= 7 u + 3 u - 30 + 50
= 10 u + 20
= 10 x 20 + 20
= 200 + 20
= 220
Answer(s): 220
