Anna has 2 containers. Container B and Container C are of different capacities. If Container B is filled by a tap at a rate of 5 litres per minute and Container C is filled by a tap at a rate of 7 litres per minute, when Container B is completely filled, 6 litres of water flowed out from Container C. If Container B is filled by a tap at a rate of 6 litres per minute and Container C is filled by a tap at a rate of 2 litres per minute, when Container B is completely filled, Container C is only one-third-filled. What is the capacity of Container C? Express your answer in litres.

	Scenario 1		Scenario 2
Container type	Container B	Container C	Container B	Container C
Volume of the container	5 u	7 u - 6	6 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.

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

Make u the same.

(1) x 7
35 u = 42 p --- (3)

(2) x 5
35 u = 30 p + 30 --- (4)

(3) = (4)
42 p = 30 p + 30
42 p - 30 p = 30
12 p = 30
1 p = 30 ÷ 12 = 2.5

Volume of Container C
= 6 p
= 6 x 2.5
= 15 ℓ

Answer(s): 15 ℓ