Question

Two pipes A and B can independently fill a tank completely in 20 and 30 minutes respectively. If both the pipes are opened simultaneously, how much time will they take to fill the tank completely?
1. 10 minutes
2. 12 minutes
3. 15 minutes
4. 25 minutes

Answer 1

Correct Answer - Option 2 : 12 minutes

Given 

Time taken by A  and B is 20 and 30 min respectively to fill a tank

Formula Used 

Work = time × efficiency 

Calculation 

Total work = LCM of 20 and 30 = 60

Efficiency of pipe A = 60/20 = 3

Efficiency of pipe B = 60/30 = 2

When Both works together , then efficiency = 3 + 2 = 5

So, total time = 60/5 = 12 mintues

∴ Both A and B will take time to fill the tank completely together is 12 min.