There are some yellow and green balls in a box. If 5 yellow balls are removed from the box, the total number of balls left will be 8 times the number of yellow balls left. If 40 green balls are removed from the box, the total number of balls left will be 3 times the number of yellow balls. How many balls are there in the box?

	Case 1		Case 2
	Yellow balls	Green balls	Yellow balls	Green balls
Before	1 u + 5	7 u	1 p	2 p + 40
Change	- 5			- 40
After	1 u	7 u	1 p	2 p

Number of green balls in the end for Case 1
= 8 u - 1 u
= 7 u

Number of yellow balls in the end for Case 2
= 3 p - 1 p
= 2 p

The number of yellow balls at first is the same for Case 1 and Case 2.
The number of green balls at first is also the same for Case 1 and Case 2.

1 u + 5 = 1 p --- (1)

7 u = 2 p + 40
7 u - 40 = 2 p --- (2)

Make p the same.

(1)_x2
2 u + 10 = 2 p --- (3)

(2) = (3)
7 u - 40 = 2 u + 10
7 u - 2 u = 10 + 40
5 u = 50

1 u = 50 ÷ 5 = 10

Number of balls in the box
= (1 u + 5) + 7 u
= 8 u + 5
= (8 x 10) + 5
= 80 + 5
= 85

Answer(s): 85