In a bag, the ratio of the number of grey marbles to the number of green marbles was 1 : 3. Each time, 5 grey and 7 green marbles were taken out of the bag. A while later, only 56 green marbles were left in the bag. What was the total number of marbles in the bag at first?
| |
Grey marbles |
Green marbles |
| Before |
1x5 =
5 u |
3x5 =
15 u |
| Change |
- 5 u |
- 7 u |
| After |
0 |
56 |
Since there is no grey marbles 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 marbles at first and taken out the same. LCM of 1 and 5 is 5.
Number of green marbles in the end
= 15 u - 7 u
= 8 u
8 u = 56
1 u = 56 ÷ 8 = 7
Total number of marbles in the bag at first
= 5 u + 15 u
= 20 u
= 20 x 7
= 140
Answer: 140
