In a bottle, the ratio of the number of green marbles to the number of gold marbles was 1 : 3. Each time, 5 green and 7 gold marbles were taken out of the bottle. A while later, only 72 gold marbles were left in the bottle. What was the total number of marbles in the bottle at first?

	Green marbles	Gold marbles
Before	1x5 = 5 u	3x5 = 15 u
Change	- 5 u	- 7 u
After	0	72

Since there is no green marbles left, this means that the number of green marbles at first is the same as the number of green marbles taken out.  

Make the number of green marbles at first and taken out the same.  LCM of 1 and 5 is 5.

Number of gold marbles in the end
= 15 u - 7 u
= 8 u

8 u = 72

1 u = 72 ÷ 8 = 9

Total number of marbles in the bottle at first
= 5 u + 15 u
= 20 u
= 20 x 9
= 180

Answer: 180