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 1/4th 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.