In a pouch, the ratio of the number of pink marbles to the number of white marbles was 1 : 3. Each time, 5 pink and 6 white marbles were taken out of the pouch. A while later, only 180 white marbles were left in the pouch. What was the total number of marbles in the pouch at first?

	Pink marbles	White marbles
Before	1x5 = 5 u	3x5 = 15 u
Change	- 5 u	- 6 u
After	0	180

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

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

Number of white marbles in the end
= 15 u - 6 u
= 9 u

9 u = 180

1 u = 180 ÷ 9 = 20

Total number of marbles in the pouch at first
= 5 u + 15 u
= 20 u
= 20 x 20
= 400

Answer: 400