Question

Pipes A and B can empty a full tank in 36 and 45 minutes, respectively, whereas pipe C alone can fill the tank in 15 minutes. B and C are opened together for 15 minutes, and then both are turned off and A is opened. Pipe A will empty the tank in (in minutes):
1. 30
2. 18
3. 20
4. 24

Answer 1

Correct Answer - Option 4 : 24

Given:

Time taken to empty a full tank by Pipe A = 36 min

Time taken to empty a full tank by Pipe B = 45 min

Time taken to fill the tank by Pipe C = 15 min

B and C opened together = 15 min

Formula used:

Work = Efficiency × Time

Calculation:

LCM of 36, 45 and 15 is 180

Efficiency of A = 180/36 = 5 units/day

Efficiency of B = 180/45 = 4 units/day

Efficiency of C = 180/15 = 12 units/day

Efficiency of B and C together = (12 – 4) = 8 units/day

B and C opened for 15 min = (8 × 15) units

⇒ 120 units

Now,

Pipe A will empty the tank = (120/5) mins

⇒ 24 mins

∴ Required time is 24 mins