Question

Water tank has three inlets, which independently can fill the tank in 20, 40, 30 minutes, respectively . How much time does it take to fill the tank when all work together.

Answer 1

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

Part filled by A in 1 min = $\frac{1}{20}$
Part filled by B in 1 min =$\frac{1}{40}$
Part filled by C in 1 min =$\frac{1}{30}$

Part filled by (A+B+C) in 1 min = $\frac{1}{20}+\frac{1}{30}+\frac{1}{40}$
$=\frac{6+4+3}{}$
=$\frac{13}{120}$

So both pipes can fill the tank in $\frac{120}{13}$ mins.=9.23 min