PSLE
Owen had 8 bottles of marbles. At first, each of the bottles contained the same number of marbles. He took 12 marbles from each bottle. After that, the total number of marbles left in the 8 bottles was equal to the total number of marbles in 2 of the bottles at first. What was the number of marbles in each bottle at first?

	2 bottles at first	Total bottles in the end
Number	2	8
Value	1 u + 12	1 u
Total value	2 u + 24	8 u

Number of marbles in each bottle in the end = 1 u
Number of marbles in each bottle at first = 1 u + 12

Number of marbles in 2 bottles at first 
= 2 x (1 u + 12)
= 2 u + 24

Total number of marbles left in the 8 bottles was equal to total number of marbles in 2 bottles at first.

8 u = 2 u + 24 
8 u - 2 u = 24
6 u = 24

1 u = 24 ÷ 6 = 4

Number of marbles in each bottle at first
= 1 u + 12
= 4 + 12
= 16

Answer(s): 16