There are 90 stickers in Container X and 40 stickers in Container Y.
Some stickers are transferred from Container X to Container Y.
Container Y has 30 more stickers than Container X.
How many stickers are transferred from Container X to Container Y?

	Container X	Container Y
Before	90	40
Change	- ?	+ ?
After	1 u	1 u + 30

Total number of stickers
= 90 + 40
= 130

In the end
Total number of stickers = 1 u + 1 u + 30 = 2 u + 30

The total number of stickers at first and in the end remains unchanged.

2 u + 30 = 130
2 u = 130 - 30 = 100

1 u = 100 ÷ 2 = 50

Number of stickers that are transferred from Container X to Container Y
= Number of stickers in Container X at first - Number of stickers in Container X in the end
= 90 - 50
= 40

Answer(s): 40