In a bottle, the ratio of the number of grey balls to the number of brown balls was 1 : 3. Each time, 4 grey and 7 brown balls were taken out of the bottle. A while later, only 130 brown balls were left in the bottle. What was the total number of balls in the bottle at first?
| |
Grey balls |
Brown balls |
| Before |
1x4 =
4 u |
3x4 =
12 u |
| Change |
- 4 u |
- 7 u |
| After |
0 |
130 |
Since there is no grey balls left, this means that the number of grey marbles at first is the same as the number of grey marbles taken out.
Make the number of grey balls at first and taken out the same. LCM of 1 and 4 is 4.
Number of brown balls in the end
= 12 u - 7 u
= 5 u
5 u = 130
1 u = 130 ÷ 5 = 26
Total number of balls in the bottle at first
= 4 u + 12 u
= 16 u
= 16 x 26
= 416
Answer: 416
