A tank can be filled in 40 minutes. ∴ In 1 minute tank is filled = 1/40 ∵ the second leak is at the centre of the tank, so until half tank is full only 1 leak will work. Bottom leak can empty the tank in 80 minutes. CALCULATION : ∴ In 1 minute, water which will leak out of tank = 1/80 ∴ In 1 minute, effective filling of tank = 1/40 – 1/80 ⇒ 1/80 ∴ Full tank will be filled in 80 minutes. Hence, 50 % of tank will be filled in 40 minutes. Now, there are two leaks in upper half of tank. ∴ effective filling of tank = 1/40 – (1/80 + 1/120) ⇒ 1/40 – 5/240 = 1/240 ∴ Full tank will be filled in 240 minutes with this rate. ∴ 50 % of tank will be filled in 120 minutes. So, the full tank will be filled in 40 + 120 = 160 minutes.