Correct Answer - Option 3 : 24 hours
Given∶
(1/5)th of the tank fills in 6 hours
Calculation∶
Remaining portion of a tank = 1 - (1/5)
⇒ 4/5
(1/5)th of a tank = 6 hours
Full tank fill = 6 × 5
⇒ 30 hours
(4/5)th tank fills = 30 × (4/5)
⇒ 24 hours
∴ 24 hours more required by pipe to fill the tank.