Question

Two taps can fill a tank in 15 and 12 minutes respectively. A third tap can empty it in 20 minutes. If all the taps are opened at the same time, then in how much time will the tank be filled?

Answer 1

Part of the tank filled when all the three taps are opened simultaneously $=\left(\frac{1}{15}+\frac{1}{12}-\frac{1}{20}\right)=\frac{4+5-3}{60}=\frac{6}{60}=\frac{1}{10}$
$\therefore$ The tank will be filled in $10$ minutes.