Question

Two pipes P and Q can fill a tank in 6 and 12 min, respectively. Starting with pipe P, both the pipes are opened alternately each for 1 minute. In how much time will the tank be filled?

1. 6 minutes
2. 8 minutes
3. 10 minutes
4. 12 minutes

Answer 1

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.