In a coin box, the ratio of the number of silver marbles to the number of grey marbles was 1 : 3. Each time, 4 silver and 7 grey marbles were taken out of the coin box. A while later, only 200 grey marbles were left in the coin box. What was the total number of marbles in the coin box at first?

	Silver marbles	Grey marbles
Before	1x4 = 4 u	3x4 = 12 u
Change	- 4 u	- 7 u
After	0	200

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

Make the number of silver marbles at first and taken out the same.  LCM of 1 and 4 is 4.

Number of grey marbles in the end
= 12 u - 7 u
= 5 u

5 u = 200

1 u = 200 ÷ 5 = 40

Total number of marbles in the coin box at first
= 4 u + 12 u
= 16 u
= 16 x 40
= 640

Answer: 640