In a bag, the ratio of the number of black balls to the number of gold balls was 1 : 3. Each time, 3 black and 7 gold balls were taken out of the bag. A while later, only 126 gold balls were left in the bag. What was the total number of balls in the bag at first?
| |
Black balls |
Gold balls |
| Before |
1x3 =
3 u |
3x3 =
9 u |
| Change |
- 3 u |
- 7 u |
| After |
0 |
126 |
Since there is no black balls left, this means that the number of black marbles at first is the same as the number of black marbles taken out.
Make the number of black balls at first and taken out the same. LCM of 1 and 3 is 3.
Number of gold balls in the end
= 9 u - 7 u
= 2 u
2 u = 126
1 u = 126 ÷ 2 = 63
Total number of balls in the bag at first
= 3 u + 9 u
= 12 u
= 12 x 63
= 756
Answer: 756
