Eric and Elijah had 67 marbles in total. Eric had 25 marbles less than Elijah at first. After Eric and Elijah played a game with Mary, Eric had ²₇ as many marbles as Elijah. If Eric lost as many marbles as Elijah to Mary, find the number of marbles that Elijah lost to Mary.

	Eric	Elijah	Difference
Before	1 u	1 u + 25	25
Change	- ?	- ?
After	2 p	7 p	5 p

Total number of marbles at first
= 1 u + 1 u + 25 
= 2 u + 25

2 u + 25 = 67
2 u = 67 - 25
2 u = 42

1 u = 42 ÷ 2 = 21

Since Eric lost the same number of marbles as Elijah, the difference in the number of marbles between Eric and Elijah at first and in the end remains the same.

Difference in the number of marbles in the end
= 7 p - 2 p
= 5 p

5 p = 25

1 p = 25 ÷ 5 = 5

Number of marbles that Eric lost to Mary
= 1 u - 2 p
= 21 - 2 x 5
= 21 - 10
= 11

Since Elijah lost the same number of marbles as Eric, the number of marbles that each lost to Mary is the same.

Number of marbles that Elijah lost = 11

Answer(s): 11