Joelle and Cindy collected cards. Joelle gave 25% of her cards to Cindy and as a result, Cindy's cards increased by 30%. If Joelle had 90 cards left, find the number of cards Cindy should give to Joelle in the end so that both had an equal number of cards.

	Joelle	Cindy	Comparing the change in Cindy's cards
Before	4x3 = 12 u		10x1 = 10u
Change	- 1x3 = - 3 u	+ 1x3 = + 3 u	+ 3x1 = + 3 u
After	3x3 = 9 u		13x1 = 13 u

25% = ²⁵₁₀₀ = ¹₄
30% = ³⁰₁₀₀ = ³₁₀

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

9 u = 90

1 u = 90 ÷ 9 = 10

Number of cards that Cindy had more than Joelle in the end
= 13 u - 9 u
= 4 u

Number of cards that Cindy should give to Joelle so that both had an equal number of cards in the end
= 4 u ÷ 2
= 2 u
= 2 x 10
= 20

Answer(s): 20