Question

Pipe A and B can fill the tank in 10 hours and 20 hours respectively where as pipe C can empty the tank in 8 hours. If all the pipes are opened together at the same time, what is the time to fill the tank ?
1. 45 hr
2. 36 hr
3. 40 hr
4. 27 hr
5. None of these

Answer 1

Correct Answer - Option 3 : 40 hr

Given:

Pipe A can fill the tank alone in 10 hours

Pipe B can fill the tank alone in 20 hours

Pipe C can empty the tank alone in 8 hours

Concept used:

Let, Pipe A can fill a tank in x hours

⇒ Pipe A can fill a tank in 1 hour = 1/x

Calculation:

Pipe A can fill in 1 hour = 1/10

Pipe B can fill in 1 hour = 1/20

Pipe C can empty in 1 hour = 1/8

The total part of the tank filled in 1 hour,

⇒ (1/10) + (1/20) - (1/8)

⇒ (4 + 2 - 5)/40

⇒ 1/40

∴ The tank will be filled in 40 hours.