Adam has 40 green stickers and 240 red stickers.
After buying the same number of stickers,
the ratio of the green stickers and the red stickers becomes 3 : 5.
How many stickers does he buy?

	Green	Red	Difference
Before	40	240	200
Change	+ ?	+ ?
After	3 u	5 u	2 u

At first
Difference in the number of stickers
= 240 - 40
= 200

In the end
Number of green stickers = 3 u
Number of red stickers = 5 u

Difference in the number of stickers in units
= 5 u - 3 u
= 2 u

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

2 u = 200

1 u = 200 ÷ 2 = 100

Number of green stickers that Adam buys
= 3 u - 40
= 3 x 100 - 40
= 300 - 40
= 260

Total number of stickers that Adam buys
= 2 x 260
= 520

Answer(s): 520