Container W contains 10 black marbles and 11 blue marbles. Container X contains 40 black marbles and 15 blue marbles. How many blue marbles and black marbles must be transferred from Container X to put into Container W so that 50% of the marbles in Container A are black and 75% of the marbles in Container X are black?

	Container W		Container X
	Black marbles	Blue marbles	Black marbles	Blue marbles
Before	10	11	40	15
Change	+ ?	+ ?	- ?	- ?
After	1 u	1 u	3 p	1 p

50% = ⁵⁰₁₀₀ = 12

75% = ⁷⁵₁₀₀ = 34

Number of black marbles = 10 + 40 = 50 

Number of blue marbles = 11 + 15 = 26 

1 u + 3 p = 50 --- (1)

1 u + 1 p = 26 ---(2)

(1) - (2)
(1 u + 3 p) - (1 u + 1 p) = 50 - 26
3 p - 1 p = 24
2 p = 24

1 p = 24 ÷ 2 = 12

From (2):
1 u + 1 p = 26
1 u + 1 x 12 = 26
1 u + 12 = 26

1 u = 26 - 12 = 14

Number of blue marbles to be transferred from Container X to Container W
= 15 - 1 p
= 15 - 1 x 12
= 15 - 12
= 3

Number of black marbles to be transferred from Container X to Container W
= 1 u - 10
= 14 - 10
= 4

Total number of blue and black marbles to be transferred from Container X to Container W
= 3 + 4
= 7

Answer(s): 7