Risa and Cathy collected stickers. Risa gave 50% of her stickers to Cathy and as a result, Cathy's stickers increased by 30%. If Risa had 21 stickers left, find the number of stickers Cathy should give to Risa in the end so that both had an equal number of stickers.

	Risa	Cathy	Comparing the change in Cathy's stickers
Before	2x3 = 6 u		10x1 = 10u
Change	- 1x3 = - 3 u	+ 1x3 = + 3 u	+ 3x1 = + 3 u
After	1x3 = 3 u		13x1 = 13 u

50% = ⁵⁰₁₀₀ = ¹₂
30% = ³⁰₁₀₀ = ³₁₀

The increase in the number of stickers that Cathy had is repeated.  Make the increase in the number of stickers that Cathy had the same. LCM of 1 and 3 = 3

3 u = 21

1 u = 21 ÷ 3 = 7

Number of stickers that Cathy had more than Risa in the end
= 13 u - 3 u
= 10 u

Number of stickers that Cathy should give to Risa so that both had an equal number of stickers in the end
= 10 u ÷ 2
= 5 u
= 5 x 7
= 35

Answer(s): 35