Amelia has 2 containers. Container M and Container N are of different capacities. If Container M is filled by a tap at a rate of 4 litres per minute and Container N is filled by a tap at a rate of 7 litres per minute, when Container M is completely filled, 5 litres of water flowed out from Container N. If Container M is filled by a tap at a rate of 4 litres per minute and Container N is filled by a tap at a rate of 2 litres per minute, when Container M is completely filled, Container N is only one-third-filled. What is the capacity of Container N? Express your answer in litres.

	Scenario 1		Scenario 2
Container type	Container M	Container N	Container M	Container N
Volume of the container	4 u	7 u - 5	4 p	2 p x 3 = 6 p

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

4 u = 4 p --- (1)
7 u - 5 = 6 p
7 u = 6 p + 5 --- (2)

Make u the same.

(1) x 7
28 u = 28 p --- (3)

(2) x 4
28 u = 24 p + 20 --- (4)

(3) = (4)
28 p = 24 p + 20
28 p - 24 p = 20
4 p = 20
1 p = 20 ÷ 4 = 5

Volume of Container N
= 6 p
= 6 x 5
= 30 ℓ

Answer(s): 30 ℓ