Box P contains 8 yellow balls and 5 silver balls. Box Q contains 135 yellow balls and 62 silver balls. How many silver balls and yellow balls must be transferred from Box Q to put into Box P so that 50% of the balls in Box A are yellow and 70% of the balls in Box Q are yellow?

	Box P		Box Q
	Yellow balls	Silver balls	Yellow balls	Silver balls
Before	8	5	135	62
Change	+ ?	+ ?	- ?	- ?
After	1 u	1 u	7 p	3 p

50% = ⁵⁰₁₀₀ = 12

70% = ⁷⁰₁₀₀ = 710

Number of yellow balls = 8 + 135 = 143 

Number of silver balls = 5 + 62 = 67 

1 u + 7 p = 143 --- (1)

1 u + 3 p = 67 ---(2)

(1) - (2)
(1 u + 7 p) - (1 u + 3 p) = 143 - 67
7 p - 3 p = 76
4 p = 76

1 p = 76 ÷ 4 = 19

From (2):
1 u + 3 p = 67
1 u + 3 x 19 = 67
1 u + 57 = 67

1 u = 67 - 57 = 10

Number of silver balls to be transferred from Box Q to Box P
= 62 - 3 p
= 62 - 3 x 19
= 62 - 57
= 5

Number of yellow balls to be transferred from Box Q to Box P
= 1 u - 8
= 10 - 8
= 2

Total number of silver and yellow balls to be transferred from Box Q to Box P
= 5 + 2
= 7

Answer(s): 7