Crate L contains 5 yellow balls and 7 green balls. Crate M contains 31 yellow balls and 14 green balls. How many green balls and yellow balls must be moved from Crate M to put into Crate L so that 50% of the balls in Crate A are yellow and 80% of the balls in Crate M are yellow?

	Crate L		Crate M
	Yellow balls	Green balls	Yellow balls	Green balls
Before	5	7	31	14
Change	+ ?	+ ?	- ?	- ?
After	1 u	1 u	4 p	1 p

50% = ⁵⁰₁₀₀ = 12

80% = ⁸⁰₁₀₀ = 45

Number of yellow balls = 5 + 31 = 36 

Number of green balls = 7 + 14 = 21 

1 u + 4 p = 36 --- (1)

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

(1) - (2)
(1 u + 4 p) - (1 u + 1 p) = 36 - 21
4 p - 1 p = 15
3 p = 15

1 p = 15 ÷ 3 = 5

From (2):
1 u + 1 p = 21
1 u + 1 x 5 = 21
1 u + 5 = 21

1 u = 21 - 5 = 16

Number of green balls to be moved from Crate M to Crate L
= 14 - 1 p
= 14 - 1 x 5
= 14 - 5
= 9

Number of yellow balls to be moved from Crate M to Crate L
= 1 u - 5
= 16 - 5
= 11

Total number of green and yellow balls to be moved from Crate M to Crate L
= 9 + 11
= 20

Answer(s): 20