Correct Answer - Option 3 : 20 minutes
Given:
All pipe together can fill the tank in 25 min
Calculation:
Let us assume pipe C can empty the tank in P min
⇒ One minute's work of A, B, and C together = 1/25
⇒ 1/30 + 2/75 - 1/P = 1/25
⇒ C alone can empty the tank in P = 50 minutes
⇒ C alone can empty the 2/5th tank in = 50 × (2/5) = 20 minutes
∴ The required result will be 20 minutes.