There are some silver and pink marbles in a box. If 10 silver marbles are removed from the box, the total number of marbles left will be 9 times the number of silver marbles left. If 20 pink marbles are removed from the box, the total number of marbles left will be 4 times the number of silver marbles. How many marbles are there in the box?

	Case 1		Case 2
	Silver marbles	Pink marbles	Silver marbles	Pink marbles
Before	1 u + 10	8 u	1 p	3 p + 20
Change	- 10			- 20
After	1 u	8 u	1 p	3 p

Number of pink marbles in the end for Case 1
= 9 u - 1 u
= 8 u

Number of silver marbles in the end for Case 2
= 4 p - 1 p
= 3 p

The number of silver marbles at first is the same for Case 1 and Case 2.
The number of pink marbles at first is also the same for Case 1 and Case 2.

1 u + 10 = 1 p --- (1)

8 u = 3 p + 20
8 u - 20 = 3 p --- (2)

Make p the same.

(1)_x3
3 u + 30 = 3 p --- (3)

(2) = (3)
8 u - 20 = 3 u + 30
8 u - 3 u = 30 + 20
5 u = 50

1 u = 50 ÷ 5 = 10

Number of marbles in the box
= (1 u + 10) + 8 u
= 9 u + 10
= (9 x 10) + 10
= 90 + 10
= 100

Answer(s): 100