Kaylee had 25% more pens than Isaiah. Anna had 50% fewer pens than Kaylee. Kaylee and Isaiah gave Anna some pens in the ratio of 3 : 5. As a result, Anna had 60% more pens than before. Given that Isaiah had 90 less pens than Anna in the end, how many pens did Isaiah give to Anna?

Kaylee	Isaiah	Anna
5x2	4x2
2x5		1x5
10	8	5

100% + 25% = 125%
125% = ¹²⁵₁₀₀ = ⁵₄

Kaylee : Isaiah = 5 : 4

100% - 50% = 50%
50% = ⁵⁰₁₀₀ = ¹₂

Kaylee : Anna = 2 : 1

The number of pens that Kaylee had at first is repeated. Make the number of pens that Kaylee had at first the same.  LCM of 5 and 2 is 10.

	Kaylee	Isaiah	Anna
Before	10x8 =  80 u	8x8 = 64 u	5x8 = 40 u
Change			+ 3x8 = + 24 u
Comparing the changes in the number of pens	- 3x3 = - 9 u	- 5x3 = - 15 u	+ 8x3 = + 24 u
After	71 u	49 u	8x8 = 64 u

60% x 5 
= ⁶⁰₁₀₀ x 5 
= 3 

The total number of pens that Kaylee and Isaiah gave to Anna is repeated.  Make the total number of pens that Kaylee and Isaiah gave to Anna the same.  LCM of 8 and 3 is 24.

Number of pens that Isaiah had less than Anna 
= 64 u - 49 u
= 15 u

15 u = 90

1 u = 90 ÷ 15 = 6

Number of pens that Isaiah gave to Anna
= 15 u
= 15 x 6
= 90

Answer(s): 90