In a jar, the ratio of the number of black balls to the number of brown balls was 1 : 3. Each time, 3 black and 7 brown balls were taken out of the jar. A while later, only 102 brown balls were left in the jar. What was the total number of balls in the jar at first?
| |
Black balls |
Brown balls |
| Before |
1x3 =
3 u |
3x3 =
9 u |
| Change |
- 3 u |
- 7 u |
| After |
0 |
102 |
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 brown balls in the end
= 9 u - 7 u
= 2 u
2 u = 102
1 u = 102 ÷ 2 = 51
Total number of balls in the jar at first
= 3 u + 9 u
= 12 u
= 12 x 51
= 612
Answer: 612
