Alexander has 2 containers. Container G and Container H are of different capacities. If Container G is filled by a tap at a rate of 3 litres per minute and Container H is filled by a tap at a rate of 7 litres per minute, when Container G is completely filled, 7 litres of water flowed out from Container H. If Container G is filled by a tap at a rate of 3 litres per minute and Container H is filled by a tap at a rate of 3 litres per minute, when Container G is completely filled, Container H is only half-filled. What is the capacity of Container H? Express your answer in litres.

	Scenario 1		Scenario 2
Container type	Container G	Container H	Container G	Container H
Volume of the container	3 u	7 u - 7	3 p	3 p x 2 = 6 p

Let 1 u be the time taken for Scenario 1.
Let 1 p be the time taken for Scenario 2.

3 u = 3 p --- (1)
7 u - 7 = 6 p
7 u = 6 p + 7 --- (2)

Make u the same.

(1) x 7
21 u = 21 p --- (3)

(2) x 3
21 u = 18 p + 21 --- (4)

(3) = (4)
21 p = 18 p + 21
21 p - 18 p = 21
3 p = 21
1 p = 21 ÷ 3 = 7

Volume of Container H
= 6 p
= 6 x 7
= 42 ℓ

Answer(s): 42 ℓ