Pipes A and B can fill a tank in 5 hours and 6 hours respectively. Another Pipe can empty the full tank in 30 hours. If all three are opened together, then the tank will be filled in :

180 minutes

The correct answer is Option (2) → 180 minutes

Rate of A = $\frac{1}{5}$ tank per hour, Rate of B = $\frac{1}{6}$ tank per hour

Rate of emptying = $-\frac{1}{30}$ tank per hour

∴ Net rate = $\frac{1}{5}+\frac{1}{6}-\frac{1}{30}$

$=\frac{10}{30}=\frac{1}{3}$ tank per hour

∵ 3 hours