Two pipes A and B can fill a tank in 30 and 20 minutes respectively. If both the pipes are used together, then how long will it take to fill the tank?

Question: Two pipes A and B can fill a tank in 30 and 20 minutes respectively. If both the pipes are used together, then how long will it take to fill the tank?

Solution:
pipe A fill a tank in 30 minutes
so, it fills in one minute (1/30)

pipe B fill a tank in 20 minutes
so, it fills in one minute (1/20)

both pipes fill in one minute = (1/30) + (1/20)
= 1/12

so, it will take 1/(1/12) or 12 minutes to fill the tank.