Maya has 2 tanks. Tank T and Tank U are of different capacities. If Tank T is filled by a tap at a rate of 3 litres per minute and Tank U is filled by a tap at a rate of 5 litres per minute, when Tank T is completely filled, 7 litres of water flowed out from Tank U. If Tank T is filled by a tap at a rate of 5 litres per minute and Tank U is filled by a tap at a rate of 2 litres per minute, when Tank T is completely filled, Tank U is only one-third-filled. What is the capacity of Tank U? Express your answer in litres.

	Scenario 1		Scenario 2
Tank type	Tank T	Tank U	Tank T	Tank U
Volume of the tank	3 u	5 u - 7	5 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.

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

Make u the same.

(1) x 5
15 u = 25 p --- (3)

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

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

Volume of Tank U
= 6 p
= 6 x 3
= 18 ℓ

Answer(s): 18 ℓ