Box H contains 6 grey marbles and 10 black marbles. Box J contains 37 grey marbles and 15 black marbles. How many black marbles and grey marbles must be transferred from Box J to put into Box H so that 50% of the marbles in Box A are grey and 75% of the marbles in Box J are grey?

	Box H		Box J
	Grey marbles	Black marbles	Grey marbles	Black marbles
Before	6	10	37	15
Change	+ ?	+ ?	- ?	- ?
After	1 u	1 u	3 p	1 p

50% = ⁵⁰₁₀₀ = 12

75% = ⁷⁵₁₀₀ = 34

Number of grey marbles = 6 + 37 = 43 

Number of black marbles = 10 + 15 = 25 

1 u + 3 p = 43 --- (1)

1 u + 1 p = 25 ---(2)

(1) - (2)
(1 u + 3 p) - (1 u + 1 p) = 43 - 25
3 p - 1 p = 18
2 p = 18

1 p = 18 ÷ 2 = 9

From (2):
1 u + 1 p = 25
1 u + 1 x 9 = 25
1 u + 9 = 25

1 u = 25 - 9 = 16

Number of black marbles to be transferred from Box J to Box H
= 15 - 1 p
= 15 - 1 x 9
= 15 - 9
= 6

Number of grey marbles to be transferred from Box J to Box H
= 1 u - 6
= 16 - 6
= 10

Total number of black and grey marbles to be transferred from Box J to Box H
= 6 + 10
= 16

Answer(s): 16