Adam has 40 green stickers and 280 red stickers.
After buying the same number of stickers,
the ratio of the green stickers and the red stickers becomes 2 : 7.
How many stickers does he buy?

	Green	Red	Difference
Before	40	280	240
Change	+ ?	+ ?
After	2 u	7 u	5 u

At first
Difference in the number of stickers
= 280 - 40
= 240

In the end
Number of green stickers = 2 u
Number of red stickers = 7 u

Difference in the number of stickers in units
= 7 u - 2 u
= 5 u

The difference in the number of stickers between the green stickers and the red stickers remains unchanged.

5 u = 240

1 u = 240 ÷ 5 = 48

Number of green stickers that Adam buys
= 2 u - 40
= 2 x 48 - 40
= 96 - 40
= 56

Total number of stickers that Adam buys
= 2 x 56
= 112

Answer(s): 112