In a bag, the ratio of the number of green balls to the number of black balls was 1 : 3. Each time, 3 green and 7 black balls were taken out of the bag. A while later, only 50 black balls were left in the bag. What was the total number of balls in the bag at first?
| |
Green balls |
Black balls |
| Before |
1x3 =
3 u |
3x3 =
9 u |
| Change |
- 3 u |
- 7 u |
| After |
0 |
50 |
Since there is no green balls left, this means that the number of green marbles at first is the same as the number of green marbles taken out.
Make the number of green balls at first and taken out the same. LCM of 1 and 3 is 3.
Number of black balls in the end
= 9 u - 7 u
= 2 u
2 u = 50
1 u = 50 ÷ 2 = 25
Total number of balls in the bag at first
= 3 u + 9 u
= 12 u
= 12 x 25
= 300
Answer: 300
