Christian had 40% more stickers than John. Isabella had 20% fewer stickers than Christian. Christian and John gave Isabella some stickers in the ratio of 1 : 3. As a result, Isabella had 50% more stickers than before. Given that Isabella had 495 more stickers than John in the end, how many stickers did Christian give to Isabella?

Christian	John	Isabella
7x5	5x5
5x7		4x7
35	25	28

100% + 40% = 140%
140% = ¹⁴⁰₁₀₀ = ⁷₅

Christian : John = 7 : 5

100% - 20% = 80%
80% = ⁸⁰₁₀₀ = ⁴₅

Christian : Isabella = 5 : 4

The number of stickers that Christian had at first is repeated. Make the number of stickers that Christian had at first the same.  LCM of 7 and 5 is 35.

	Christian	John	Isabella
Before	35x2 =  70 u	25x2 = 50 u	28x2 = 56 u
Change			+ 14x2 = + 28 u
Comparing the changes in the number of stickers	- 1x7 = - 7 u	- 3x7 = - 21 u	+ 4x7 = + 28 u
After	63 u	29 u	42x2 = 84 u

50% x 28 
= ⁵⁰₁₀₀ x 28 
= 14 

The total number of stickers that Christian and John gave to Isabella is repeated.  Make the total number of stickers that Christian and John gave to Isabella the same.  LCM of 4 and 14 is 28.

Number of stickers that Isabella had more than John 
= 84 u - 29 u
= 55 u

55 u = 495

1 u = 495 ÷ 55 = 9

Number of stickers that Christian gave to Isabella
= 7 u
= 7 x 9
= 63

Answer(s): 63