PSLE
Valen had 10 bottles of beads. At first, each of the bottles contained the same number of beads. He took 18 beads from each bottle. After that, the total number of beads left in the 10 bottles was equal to the total number of beads in 4 of the bottles at first. What was the number of beads in each bottle at first?

	4 bottles at first	Total bottles in the end
Number	4	10
Value	1 u + 18	1 u
Total value	4 u + 72	10 u

Number of beads in each bottle in the end = 1 u
Number of beads in each bottle at first = 1 u + 18

Number of beads in 4 bottles at first 
= 4 x (1 u + 18)
= 4 u + 72

Total number of beads left in the 10 bottles was equal to total number of beads in 4 bottles at first.

10 u = 4 u + 72 
10 u - 4 u = 72
6 u = 72

1 u = 72 ÷ 6 = 12

Number of beads in each bottle at first
= 1 u + 18
= 12 + 18
= 30

Answer(s): 30