Number of minutes Pipe A requires to fill an empty tank : 20 minutes

Number of minutes Pipe B requires to fill an empty tank : 30 minutes

Amount of water filled by Pipe A in empty tank in one minute: \(\frac{1}{20}\)

Amount of water filled by Pipe B in one minute: \(\frac{1}{30}\)

Amount of water filled by Pipe A and Pipe B together in one minute:

\(\frac{1}{20}+\frac{1}{30}=\frac{5}{60}=\frac{1}{12}\)

∴ They can fill the tank together in 12 minutes.