Question

Two pipes can fill a tank in 10 hours and 12 hours respectively while the third pipe empties the tank in 20 hours. If all the three pipes operate simultaneously, in how much time will the tank be filled ?
1. 7 hours 30 minutes
2. 7 hours
3. 6 hours 30 minutes
4. 2 hours

Answer 1

Correct Answer - Option 1 : 7 hours 30 minutes

Given:

Time taken to fill a tank by pipe A = 10 hours

Time taken to fill a tank by Pipe B = 12 hours

Time taken to empty the tank by Pipe C = 20 hours

Calculation:

Let in x hours the tank will be filled by 3 pipes

In 1 hour the first pipe can fill = 1/10 units

In 1 hour the second pipe can fill = 1/12 units

In 1 hour the third pipe can empty the tank = 1/20 units

According to question

⇒ x/10 + x/12 – x/20 = 1

⇒ (6x + 5x – 3x)/60 = 1

⇒ 8x/60 = 1

⇒ x = 7.5 hours

∴ The tank will be filled in 7 hours 30 minutes