Pipe 'P' can fill a tank in 36 hours and pipe 'Q' can fill this tank in 45 hours. If both the pipes are opened simultaneously, then how much time will be taken to fill this tank ?
Required answerÂ
= $$ \frac{1}{36} + \frac{1}{45} = \frac{81}{36 \times 45} = \frac{1}{20}$$
If both the pipes are opened simultaneously, then 20 hrs will be taken to fill this tank.
So, the answer would be option a)20 hours
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