A Pipe P can fill a tank in 16 minutes and the other pipe Q can empty the whole tank in 32 minutes. If both P and Q are opened simultaneously then the time taken to fill the tank is -

Let X hours be the time taken to fill a tank by P.
Let Y hours be the time taken to empty the tank by Q.
Then the time taken to fill the tank when P and Q are switched together : XY/(Y - X) hours.
Here, X = 16 minutes And Y = 32 minutes
Therefore,
Required time = (16 × 32)/(32 - 16)
= (32 × 16)/16
= 32 minutes.