Correct Answer - Option 2 : 10 min

**Given:**

A pipe of diameter d can empty the tank in 40 minutes

**Formula used:**

Area of a circle = πr^{2}

Work done = Time × Efficiency

**Calculation:**

Total work done by the pipe with the diameter d

40 × π(d/2)^{2} = 10πd^{2}

Now the diameter is doubled

So the time to empty the tank is

Time = \(\dfrac{10πd^2}{\pi (\frac{2d}{2})^2}\)

⇒ Time = 10 minutes

**∴ The pipe with double the diameter will empty the tank in 10 minutes. **