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

	Lynn	Cindy	Comparing the change in Cindy's postcards
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 postcards that Cindy had is repeated.  Make the increase in the number of postcards that Cindy had the same. LCM of 1 and 3 = 3

3 u = 30

1 u = 30 ÷ 3 = 10

Number of postcards that Cindy had more than Lynn in the end
= 13 u - 3 u
= 10 u

Number of postcards that Cindy should give to Lynn so that both had an equal number of postcards in the end
= 10 u ÷ 2
= 5 u
= 5 x 10
= 50

Answer(s): 50