Box C contains 3 purple balls and 7 white balls. Box D contains 23 purple balls and 11 white balls. How many white balls and purple balls must be transferred from Box D to put into Box C so that 50% of the balls in Box A are purple and 70% of the balls in Box D are purple?

	Box C		Box D
	Purple balls	White balls	Purple balls	White balls
Before	3	7	23	11
Change	+ ?	+ ?	- ?	- ?
After	1 u	1 u	7 p	3 p

50% = ⁵⁰₁₀₀ = 12

70% = ⁷⁰₁₀₀ = 710

Number of purple balls = 3 + 23 = 26 

Number of white balls = 7 + 11 = 18 

1 u + 7 p = 26 --- (1)

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

(1) - (2)
(1 u + 7 p) - (1 u + 3 p) = 26 - 18
7 p - 3 p = 8
4 p = 8

1 p = 8 ÷ 4 = 2

From (2):
1 u + 3 p = 18
1 u + 3 x 2 = 18
1 u + 6 = 18

1 u = 18 - 6 = 12

Number of white balls to be transferred from Box D to Box C
= 11 - 3 p
= 11 - 3 x 2
= 11 - 6
= 5

Number of purple balls to be transferred from Box D to Box C
= 1 u - 3
= 12 - 3
= 9

Total number of white and purple balls to be transferred from Box D to Box C
= 5 + 9
= 14

Answer(s): 14