In a jar, the ratio of the number of red marbles to the number of black marbles was 1 : 3. Each time, 4 red and 6 black marbles were taken out of the jar. A while later, only 120 black marbles were left in the jar. What was the total number of marbles in the jar at first?
| |
Red marbles |
Black marbles |
| Before |
1x4 =
4 u |
3x4 =
12 u |
| Change |
- 4 u |
- 6 u |
| After |
0 |
120 |
Since there is no red marbles left, this means that the number of red marbles at first is the same as the number of red marbles taken out.
Make the number of red marbles at first and taken out the same. LCM of 1 and 4 is 4.
Number of black marbles in the end
= 12 u - 6 u
= 6 u
6 u = 120
1 u = 120 ÷ 6 = 20
Total number of marbles in the jar at first
= 4 u + 12 u
= 16 u
= 16 x 20
= 320
Answer: 320
