Two pipes A and B can independently fill a tank completely in 20 and 30 minutes respectively. If both the pipes are opened simultaneously, how much time will they take to fill the tank completely?
Let capacity of tank be 60 litres (LCM of 20 & 30)
Pipe A can fill 3 litres in one minute. Pipe B can fill 2 litres in one minute.
Both pipes can fill 5 litres in one minute.
Time required = 60/5 = 12 minutes
The correct option is C.