Ben had three bags of black beans, K, L and M and the mass of each bag of black beans was in the ratio 3 : 1 : 5. Ben decided to transfer 30% of black beans from Bag K into Bag L and 70% of black beans from Bag M into Bag L. Given that the mass of Bag L was 21.6 kg in the end, how many kilograms of black beans were transferred into Bag L?

	K	L	M
Before	3 u	1 u	5 u
Change 1	- 0.9 u	+ 0.9 u
Change 2		+ 3.5 u	- 3.5 u
After	2.1 u	5.4 u	1.5 u

Mass of black beans transferred from Bag K into Bag L
= 30% x 3 u
= ³⁰₁₀₀ x 3 u
= 2.1 u

Mass of black beans transferred from Bag M into Bag L
= 70% x 5 u
= ⁷⁰₁₀₀ x 5 u
= 3.5 u

Mass of black beans in Bag L in the end
= 1 u + 0.9 u + 3.5 u
= 5.4 u

5.4 u = 21.6 

1 u = 21.6 ÷ 5.4 = 4

Mass of black beans transferred into Bag L
= 0.9 u + 3.5 u
= 4.4 u
= 4.4 x 4
= 17.6 kg

Answer(s): 17.6 kg