Box J contains 12 silver balls and 7 gold balls. Box K contains 17 silver balls and 14 gold balls. How many gold balls and silver balls must be removed from Box K to put into Box J so that 50% of the balls in Box A are silver and 70% of the balls in Box K are silver?

	Box J		Box K
	Silver balls	Gold balls	Silver balls	Gold balls
Before	12	7	17	14
Change	+ ?	+ ?	- ?	- ?
After	1 u	1 u	7 p	3 p

50% = ⁵⁰₁₀₀ = 12

70% = ⁷⁰₁₀₀ = 710

Number of silver balls = 12 + 17 = 29 

Number of gold balls = 7 + 14 = 21 

1 u + 7 p = 29 --- (1)

1 u + 3 p = 21 ---(2)

(1) - (2)
(1 u + 7 p) - (1 u + 3 p) = 29 - 21
7 p - 3 p = 8
4 p = 8

1 p = 8 ÷ 4 = 2

From (2):
1 u + 3 p = 21
1 u + 3 x 2 = 21
1 u + 6 = 21

1 u = 21 - 6 = 15

Number of gold balls to be removed from Box K to Box J
= 14 - 3 p
= 14 - 3 x 2
= 14 - 6
= 8

Number of silver balls to be removed from Box K to Box J
= 1 u - 12
= 15 - 12
= 3

Total number of gold and silver balls to be removed from Box K to Box J
= 8 + 3
= 11

Answer(s): 11