Question

Two pipes A and B can fill a tank in 20 and 30 minutes respectively. If both the pipes are used together, then how long will it take to fill the tank?

Answer 1

In this type of questions we first get the filling in 1 minute for both pipes then we will add them to get the result, as

Part filled by A in 1 min = 1/20
Part filled by B in 1 min = 1/30

Part filled by (A+B) in 1 min = 1/20 + 1/30
= 1/12

So both pipes can fill the tank in 12 mins.

Answer 2

Part filled by A in 1 min =1/20

Part filled by B in 1 min =1/30

Part filled by (A + B) in 1 min =1/20+1/30 = 1/12

 Both pipes can fill the tank in 12 minutes.