In a jar, the ratio of the number of grey marbles to the number of silver marbles was 1 : 4. Each time, 3 grey and 6 silver marbles were taken out of the jar. A while later, only 150 silver marbles were left in the jar. What was the total number of marbles in the jar at first?

	Grey marbles	Silver marbles
Before	1x3 = 3 u	4x3 = 12 u
Change	- 3 u	- 6 u
After	0	150

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 3 is 3.

Number of silver marbles in the end
= 12 u - 6 u
= 6 u

6 u = 150

1 u = 150 ÷ 6 = 25

Total number of marbles in the jar at first
= 3 u + 12 u
= 15 u
= 15 x 25
= 375

Answer: 375