Cody and Vaidev had 61 stickers in total. Cody had 21 stickers less than Vaidev at first. After Cody and Vaidev played a game with Xylia, Cody had ¹₈ as many stickers as Vaidev. If Cody lost as many stickers as Vaidev to Xylia, find the number of stickers that Vaidev lost to Xylia.

	Cody	Vaidev	Difference
Before	1 u	1 u + 21	21
Change	- ?	- ?
After	1 p	8 p	7 p

Total number of stickers at first
= 1 u + 1 u + 21 
= 2 u + 21

2 u + 21 = 61
2 u = 61 - 21
2 u = 40

1 u = 40 ÷ 2 = 20

Since Cody lost the same number of stickers as Vaidev, the difference in the number of stickers between Cody and Vaidev at first and in the end remains the same.

Difference in the number of stickers in the end
= 8 p - 1 p
= 7 p

7 p = 21

1 p = 21 ÷ 7 = 3

Number of stickers that Cody lost to Xylia
= 1 u - 1 p
= 20 - 1 x 3
= 20 - 3
= 17

Since Vaidev lost the same number of stickers as Cody, the number of stickers that each lost to Xylia is the same.

Number of stickers that Vaidev lost = 17

Answer(s): 17