In a tin can, the ratio of the number of brown marbles to the number of pink marbles was 1 : 3. Each time, 3 brown and 7 pink marbles were taken out of the tin can. A while later, only 48 pink marbles were left in the tin can. What was the total number of marbles in the tin can at first?

	Brown marbles	Pink marbles
Before	1x3 = 3 u	3x3 = 9 u
Change	- 3 u	- 7 u
After	0	48

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

Make the number of brown marbles at first and taken out the same.  LCM of 1 and 3 is 3.

Number of pink marbles in the end
= 9 u - 7 u
= 2 u

2 u = 48

1 u = 48 ÷ 2 = 24

Total number of marbles in the tin can at first
= 3 u + 9 u
= 12 u
= 12 x 24
= 288

Answer: 288