Levi had 50% more erasers than Riordan. Lily had 20% fewer erasers than Levi. Levi and Riordan gave Lily some erasers in the ratio of 4 : 5. As a result, Lily had 25% more erasers than before. Given that Lily had 60 more erasers than Riordan in the end, how many erasers did Levi give to Lily?

Levi	Riordan	Lily
3x5	2x5
5x3		4x3
15	10	12

100% + 50% = 150%
150% = ¹⁵⁰₁₀₀ = ³₂

Levi : Riordan = 3 : 2

100% - 20% = 80%
80% = ⁸⁰₁₀₀ = ⁴₅

Levi : Lily = 5 : 4

The number of erasers that Levi had at first is repeated. Make the number of erasers that Levi had at first the same.  LCM of 3 and 5 is 15.

	Levi	Riordan	Lily
Before	15x3 =  45 u	10x3 = 30 u	12x3 = 36 u
Change			+ 3x3 = + 9 u
Comparing the changes in the number of erasers	- 4x1 = - 4 u	- 5x1 = - 5 u	+ 9x1 = + 9 u
After	41 u	25 u	15x3 = 45 u

25% x 12 
= ²⁵₁₀₀ x 12 
= 3 

The total number of erasers that Levi and Riordan gave to Lily is repeated.  Make the total number of erasers that Levi and Riordan gave to Lily the same.  LCM of 9 and 3 is 9.

Number of erasers that Lily had more than Riordan 
= 45 u - 25 u
= 20 u

20 u = 60

1 u = 60 ÷ 20 = 3

Number of erasers that Levi gave to Lily
= 4 u
= 4 x 3
= 12

Answer(s): 12