Harper has 2 tanks. Tank D and Tank E are of different capacities. If Tank D is filled by a tap at a rate of 3 litres per minute and Tank E is filled by a tap at a rate of 7 litres per minute, when Tank D is completely filled, 8 litres of water flowed out from Tank E. If Tank D is filled by a tap at a rate of 6 litres per minute and Tank E is filled by a tap at a rate of 2 litres per minute, when Tank D is completely filled, Tank E is only one-fifth-filled. What is the capacity of Tank E? Express your answer in litres.

	Scenario 1		Scenario 2
Tank type	Tank D	Tank E	Tank D	Tank E
Volume of the tank	3 u	7 u - 8	6 p	2 p x 5 = 10 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)
7 u - 8 = 10 p
7 u = 10 p + 8 --- (2)

Make u the same.

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

(2) x 3
21 u = 30 p + 24 --- (4)

(3) = (4)
42 p = 30 p + 24
42 p - 30 p = 24
12 p = 24
1 p = 24 ÷ 12 = 2

Volume of Tank E
= 10 p
= 10 x 2
= 20 ℓ

Answer(s): 20 ℓ