Cody had three bags of potato starch, R, S and T and the mass of each bag of potato starch was in the ratio 3 : 2 : 1. Cody decided to transfer 10% of potato starch from Bag R into Bag S and 80% of potato starch from Bag T into Bag S. Given that the mass of Bag S was 12.4 kg in the end, how many kilograms of potato starch were transferred into Bag S?

	R	S	T
Before	3 u	2 u	1 u
Change 1	- 0.3 u	+ 0.3 u
Change 2		+ 0.8 u	- 0.8 u
After	2.7 u	3.1 u	0.2 u

Mass of potato starch transferred from Bag R into Bag S
= 10% x 3 u
= ¹⁰₁₀₀ x 3 u
= 2.7 u

Mass of potato starch transferred from Bag T into Bag S
= 80% x 1 u
= ⁸⁰₁₀₀ x 1 u
= 0.8 u

Mass of potato starch in Bag S in the end
= 2 u + 0.3 u + 0.8 u
= 3.1 u

3.1 u = 12.4 

1 u = 12.4 ÷ 3.1 = 4

Mass of potato starch transferred into Bag S
= 0.3 u + 0.8 u
= 1.1 u
= 1.1 x 4
= 4.4 kg

Answer(s): 4.4 kg