Seth had an equal number of strawberry cookies, vanila cookies and butter cookies. After he ate 33 strawberry cookies, some vanila cookies and butter cookies, there were 57 cookies left. The number of vanila cookies he ate was twice the number of butter cookies he ate. The number of vanila cookies left was 13 more than the number of strawberry cookies left. How many strawberry cookies were there at first?

	Strawberry cookies	Vanila cookies	Butter cookies	Total cookies
Before	1 p + 33	1 p + 2 u + 13	1 p + 2 u + 13
Change	- 33	- 2 u	- 1 u
After	1 p	1 p + 13	1 p + 13 + 1 u	57

Number of vanila cookies and strawberry cookies was equal at first.

1 p + 2 u + 13 = 1 p + 33
2 u = 33 - 13
2 u = 20

1 u = 20 ÷ 2 = 10

Total number of cookies in the end
= 1 p + 1 p + 13 + 1 p + 13 + 10
= 1 p + 1 p + 1 p + 13 + 13 + 10
= 3 p + 36

3 p + 36 = 57
3 p = 57 - 36
3 p = 21

1 p = 21 ÷ 3 = 7

Number of strawberry cookies at first
= 1 p + 33
= 7 + 33
= 40

Answer(s): 40