Adam has 40 blue stickers and 300 green stickers.
After buying the same number of stickers,
the ratio of the blue stickers and the green stickers becomes 3 : 7.
How many stickers does he buy?

	Blue	Green	Difference
Before	40	300	260
Change	+ ?	+ ?
After	3 u	7 u	4 u

At first
Difference in the number of stickers
= 300 - 40
= 260

In the end
Number of blue stickers = 3 u
Number of green stickers = 7 u

Difference in the number of stickers in units
= 7 u - 3 u
= 4 u

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

4 u = 260

1 u = 260 ÷ 4 = 65

Number of blue stickers that Adam buys
= 3 u - 40
= 3 x 65 - 40
= 195 - 40
= 155

Total number of stickers that Adam buys
= 2 x 155
= 310

Answer(s): 310