Question

Two pipes can fill a tank in 20 minutes and 30 minutes respectively. If both the pipes are opened simultaneously, in how many minutes the tank will be filled ?

Answer 1

Part filled by both pipes in 1 min = $(\frac{1}{20}+\frac{1}{30})=\frac{5}{60}=\frac{1}{12}$

Time taken to fill the tank = 12 minutes