Question

A tap can empty a tank in one hour A second tap can empty it in 30 minutes. If both the taps operate simultaneously, how much time is needed to empty the tank?

1. 20 min
2. 30 min
3. 40 min
4. 45 min

Answer 1

Correct Answer - Option 1 : 20 min

Given

A tap can empty a tank in one hour A second tap can empty it in 30 minutes. 

Concept used

Pipe and Cistern

Calculation

Let us take tap A emptys the tank in 60 minutes

Tap B takes 30 minutes

Total time = Lcm of 30 and 60 

Total time = 60 units

Efficiency of Tap A = 60/60 = 1 unit

Efficiency of Tap B = 60/30 = 2 units

Together time they take 

⇒ 60 / (1 + 2)

⇒ 20 minutes