Question

Two pipe A and B can fill a tank in 10 hour and 12 hour respectively. Another pipe C can empty the same tank in 5 hour. In how many times the tank will be empty if all pipes are open?
1. 15 hour
2. 8 hour
3. 60 hour
4. 30 hour

Answer 1

Correct Answer - Option 3 : 60 hour

Given:

 A and B can fill a tank in 10 hour and 12 hour respectively.

C can empty the same tank in 5 hour.

Formula used:

Total work = Efficiency × Time

Calculation:

Efficiency of A = (1/10) unit/day

Efficiency of B = (1/12) unit/day

Efficiency of C = (1/5) unit/day

Work done by (A + B - C) in one day = (1/10) + (1/12) - (1/5) unit

⇒ (6 + 5 - 12)/60 unit

⇒ -1/60 unit

So, 1 unit will be empty if all pipes are open for 1 hour.

Then, Total time = 1/(1/60) hours

⇒ 60 hours

∴ Tank will be empty in 60 hour if all the pipes are open.