Evelyn has 2 tanks. Tank L and Tank M are of different capacities. If Tank L is filled by a tap at a rate of 3 litres per minute and Tank M is filled by a tap at a rate of 5 litres per minute, when Tank L is completely filled, 6 litres of water flowed out from Tank M. If Tank L is filled by a tap at a rate of 6 litres per minute and Tank M is filled by a tap at a rate of 3 litres per minute, when Tank L is completely filled, Tank M is only half-filled. What is the capacity of Tank M? Express your answer in litres.

	Scenario 1		Scenario 2
Tank type	Tank L	Tank M	Tank L	Tank M
Volume of the tank	3 u	5 u - 6	6 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 = 6 p --- (1)
5 u - 6 = 6 p
5 u = 6 p + 6 --- (2)

Make u the same.

(1) x 5
15 u = 30 p --- (3)

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

(3) = (4)
30 p = 18 p + 18
30 p - 18 p = 18
12 p = 18
1 p = 18 ÷ 12 = 1.5

Volume of Tank M
= 6 p
= 6 x 1.5
= 9 ℓ

Answer(s): 9 ℓ