Adam has 70 red stickers and 300 blue stickers.
After buying the same number of stickers,
the ratio of the red stickers and the blue stickers becomes 3 : 5.
How many stickers does he buy?

	Red	Blue	Difference
Before	70	300	230
Change	+ ?	+ ?
After	3 u	5 u	2 u

At first
Difference in the number of stickers
= 300 - 70
= 230

In the end
Number of red stickers = 3 u
Number of blue 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 red stickers and the blue stickers remains unchanged.

2 u = 230

1 u = 230 ÷ 2 = 115

Number of red stickers that Adam buys
= 3 u - 70
= 3 x 115 - 70
= 345 - 70
= 275

Total number of stickers that Adam buys
= 2 x 275
= 550

Answer(s): 550