Riordan had three bags of potato starch, L, M and N and the mass of each bag of potato starch was in the ratio 1 : 3 : 3. Riordan decided to transfer 40% of potato starch from Bag L into Bag M and 70% of potato starch from Bag N into Bag M. Given that the mass of Bag M was 27.5 kg in the end, how many kilograms of potato starch were transferred into Bag M?

	L	M	N
Before	1 u	3 u	3 u
Change 1	- 0.4 u	+ 0.4 u
Change 2		+ 2.1 u	- 2.1 u
After	0.6 u	5.5 u	0.9 u

Mass of potato starch transferred from Bag L into Bag M
= 40% x 1 u
= ⁴⁰₁₀₀ x 1 u
= 0.6 u

Mass of potato starch transferred from Bag N into Bag M
= 70% x 3 u
= ⁷⁰₁₀₀ x 3 u
= 2.1 u

Mass of potato starch in Bag M in the end
= 3 u + 0.4 u + 2.1 u
= 5.5 u

5.5 u = 27.5 

1 u = 27.5 ÷ 5.5 = 5

Mass of potato starch transferred into Bag M
= 0.4 u + 2.1 u
= 2.5 u
= 2.5 x 5
= 12.5 kg

Answer(s): 12.5 kg