Box S contains 9 brown marbles and 11 grey marbles. Box T contains 23 brown marbles and 11 grey marbles. How many grey marbles and brown marbles must be moved from Box T to put into Box S so that 50% of the marbles in Box A are brown and 75% of the marbles in Box T are brown?

	Box S		Box T
	Brown marbles	Grey marbles	Brown marbles	Grey marbles
Before	9	11	23	11
Change	+ ?	+ ?	- ?	- ?
After	1 u	1 u	3 p	1 p

50% = ⁵⁰₁₀₀ = 12

75% = ⁷⁵₁₀₀ = 34

Number of brown marbles = 9 + 23 = 32 

Number of grey marbles = 11 + 11 = 22 

1 u + 3 p = 32 --- (1)

1 u + 1 p = 22 ---(2)

(1) - (2)
(1 u + 3 p) - (1 u + 1 p) = 32 - 22
3 p - 1 p = 10
2 p = 10

1 p = 10 ÷ 2 = 5

From (2):
1 u + 1 p = 22
1 u + 1 x 5 = 22
1 u + 5 = 22

1 u = 22 - 5 = 17

Number of grey marbles to be moved from Box T to Box S
= 11 - 1 p
= 11 - 1 x 5
= 11 - 5
= 6

Number of brown marbles to be moved from Box T to Box S
= 1 u - 9
= 17 - 9
= 8

Total number of grey and brown marbles to be moved from Box T to Box S
= 6 + 8
= 14

Answer(s): 14