In a pouch, the ratio of the number of black balls to the number of blue balls was 1 : 4. Each time, 4 black and 6 blue balls were taken out of the pouch. A while later, only 120 blue balls were left in the pouch. What was the total number of balls in the pouch at first?
| |
Black balls |
Blue balls |
| Before |
1x4 =
4 u |
4x4 =
16 u |
| Change |
- 4 u |
- 6 u |
| After |
0 |
120 |
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 4 is 4.
Number of blue balls in the end
= 16 u - 6 u
= 10 u
10 u = 120
1 u = 120 ÷ 10 = 12
Total number of balls in the pouch at first
= 4 u + 16 u
= 20 u
= 20 x 12
= 240
Answer: 240
