Question

Two pipes A and B can fill a water tank in 24 minutes and 48 minutes respectively. If both the pipes are opened simultaneously, then after what time the pipe B must be closed so that tank will be filled in 16 minutes?
1. 8
2. 10
3. 12
4. 16

Answer 1

Correct Answer - Option 4 : 16

Given 

Pipe A can fill the tank = 24 minutes 

Pipe B can fill the tank = 48 minutes 

Formula Used

Work = Time × Efficiency

Calculation

LCM of (24, 48) = 48

Let the total work be 48 

Efficiency of A = 48/24 = 2/minutes

Efficiency of B = 48/48 = 1/minutes

Work done by A in 16 minutes = 2 × 16 = 32 

Remaining work can be done by B = 16/1 = 16 minutes 

∴ B must be closed in 16 minutes so that tank will be filled in 16 minutes