Shiyun and Elyse had a total of 84 erasers. Elyse gave ¹₅ of her erasers to Shiyun. In return, Shiyun gave ¹₈ of the total number of erasers that she had to Elyse. In the end, each girl had the same number of erasers. How many erasers did Shiyun have at first?

	Shiyun	Elyse	Total
Before 1	?	5 u	84
Change 1	+ 1 u	- 1 u
After 1	48	4 u	84
Before 2	8 p	4 u	84
Change 2	- 1 p	+ 1 p
After 2	7 p (42)	42	84

Since Elyse gave some erasers to Shiyun and Shiyun then gave some erasers to Elyse, it is an internal transfer of erasers between the two girls. So, the total number of erasers remains unchanged.

Number of erasers that Elyse and Shiyun each had in the end is the same.

Number of erasers that Shiyun had in the end
= 84 ÷ 2
= 42

Number of erasers that Shiyun had in the end = 7 p

7 p = 42

1 p = 42 ÷ 7 = 6

Number of erasers that Shiyun had after receiving some erasers from Elyse
= 8 p
= 8 x 6
= 48

Number of erasers that Elyse had after giving to Shiyun
= 84 - 48
= 36

4 u = 36

1 u = 36 ÷ 4 = 9

Number of erasers that Elyse had at first
= 5 u
= 5 x 9
= 45

Number of erasers that Shiyun had at first
= 84 - 45
= 39

Answer(s): 39