Ivan had three bags of red beans, U, V and W and the mass of each bag of red beans was in the ratio 1 : 2 : 1. Ivan decided to transfer 30% of red beans from Bag U into Bag V and 70% of red beans from Bag W into Bag V. Given that the mass of Bag V was 21 kg in the end, how many kilograms of red beans were transferred into Bag V?

	U	V	W
Before	1 u	2 u	1 u
Change 1	- 0.3 u	+ 0.3 u
Change 2		+ 0.7 u	- 0.7 u
After	0.7 u	3 u	0.3 u

Mass of red beans transferred from Bag U into Bag V
= 30% x 1 u
= ³⁰₁₀₀ x 1 u
= 0.7 u

Mass of red beans transferred from Bag W into Bag V
= 70% x 1 u
= ⁷⁰₁₀₀ x 1 u
= 0.7 u

Mass of red beans in Bag V in the end
= 2 u + 0.3 u + 0.7 u
= 3 u

3 u = 21 

1 u = 21 ÷ 3 = 7

Mass of red beans transferred into Bag V
= 0.3 u + 0.7 u
= 1 u
= 1 x 7
= 7 kg

Answer(s): 7 kg