Correct Answer - Option 2 : 8 minutes

**Given:**

Pipe P takes = 6 min

Pipe Q takes = 12 min

**Calculation:**

Part filled by Pipe P in 1 min = 1/6

Part filled by Pipe Q in 1 min = 1/12

Part filled by (P + Q) in 2 min = 1/6 + 1/12

⇒ (2 + 1)/12

⇒ 3/12

⇒ 1/4

As 1/4^{th} part is filled in 2 min.

The full tank will be filled in = 4 × 2

⇒ 8 minutes.

**∴** **The tank will be filled in 8 minutes.**