A pipe can fill a tank in 20 minutes and together pipe can empty the same tank in 60 minutes. If both the pipes are opened together, then find how much time will they take to fill the tank ?

30 min

The correct answer is option (3) : 30 min

Part of the tank filled by 1st pipe in 1 min $=\frac{1}{20}$

Part of tank emptied by second pipe in 1 min $=\frac{1}{60}$

∴ Part of tak filled by both the pipes in 1 min $=\frac{1}{20}-\frac{1}{60}=\frac{1}{30}$

∴ The time taken to fill the tank $=30\, min $