Erika and Min collected marbles. Erika gave 50% of her marbles to Min and as a result, Min's marbles increased by 30%. If Erika had 18 marbles left, find the number of marbles Min should give to Erika in the end so that both had an equal number of marbles.

	Erika	Min	Comparing the change in Min's marbles
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 marbles that Min had is repeated.  Make the increase in the number of marbles that Min had the same. LCM of 1 and 3 = 3

3 u = 18

1 u = 18 ÷ 3 = 6

Number of marbles that Min had more than Erika in the end
= 13 u - 3 u
= 10 u

Number of marbles that Min should give to Erika so that both had an equal number of marbles in the end
= 10 u ÷ 2
= 5 u
= 5 x 6
= 30

Answer(s): 30