Box D contains 7 blue marbles and 16 green marbles. Box E contains 30 blue marbles and 9 green marbles. How many green marbles and blue marbles must be removed from Box E to put into Box D so that 50% of the marbles in Box A are blue and 75% of the marbles in Box E are blue?

	Box D		Box E
	Blue marbles	Green marbles	Blue marbles	Green marbles
Before	7	16	30	9
Change	+ ?	+ ?	- ?	- ?
After	1 u	1 u	3 p	1 p

50% = ⁵⁰₁₀₀ = 12

75% = ⁷⁵₁₀₀ = 34

Number of blue marbles = 7 + 30 = 37 

Number of green marbles = 16 + 9 = 25 

1 u + 3 p = 37 --- (1)

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

(1) - (2)
(1 u + 3 p) - (1 u + 1 p) = 37 - 25
3 p - 1 p = 12
2 p = 12

1 p = 12 ÷ 2 = 6

From (2):
1 u + 1 p = 25
1 u + 1 x 6 = 25
1 u + 6 = 25

1 u = 25 - 6 = 19

Number of green marbles to be removed from Box E to Box D
= 9 - 1 p
= 9 - 1 x 6
= 9 - 6
= 3

Number of blue marbles to be removed from Box E to Box D
= 1 u - 7
= 19 - 7
= 12

Total number of green and blue marbles to be removed from Box E to Box D
= 3 + 12
= 15

Answer(s): 15