Box D contains 9 silver marbles and 8 white marbles. Box E contains 69 silver marbles and 22 white marbles. How many white marbles and silver marbles must be moved from Box E to put into Box D so that 50% of the marbles in Box A are silver and 80% of the marbles in Box E are silver?

	Box D		Box E
	Silver marbles	White marbles	Silver marbles	White marbles
Before	9	8	69	22
Change	+ ?	+ ?	- ?	- ?
After	1 u	1 u	4 p	1 p

50% = ⁵⁰₁₀₀ = 12

80% = ⁸⁰₁₀₀ = 45

Number of silver marbles = 9 + 69 = 78 

Number of white marbles = 8 + 22 = 30 

1 u + 4 p = 78 --- (1)

1 u + 1 p = 30 ---(2)

(1) - (2)
(1 u + 4 p) - (1 u + 1 p) = 78 - 30
4 p - 1 p = 48
3 p = 48

1 p = 48 ÷ 3 = 16

From (2):
1 u + 1 p = 30
1 u + 1 x 16 = 30
1 u + 16 = 30

1 u = 30 - 16 = 14

Number of white marbles to be moved from Box E to Box D
= 22 - 1 p
= 22 - 1 x 16
= 22 - 16
= 6

Number of silver marbles to be moved from Box E to Box D
= 1 u - 9
= 14 - 9
= 5

Total number of white and silver marbles to be moved from Box E to Box D
= 6 + 5
= 11

Answer(s): 11