A tap can empty a tank in one hour. A second tap can empty it in 30 minutes. If both the taps operate simultaneously, how much time is needed to empty the tank?

A tap can empty a tank in one hour. A second tap can empty it in 30 minutes. If both the taps operate simultaneously, how much time is needed to empty the tank?
[A]45 minutes
[B]20 minutes
[C]40 minutes
[D]30 minutes

20 minutes
1 hour = 60 minutes
Rate of emptying the tank by the two taps are \frac{1}{60} and \frac{1}{30} of the tank per minute respectively.
Rate of emptying the tank when both operate simultaneously =
= \frac{1}{60} + \frac{1}{30} = \frac{1+2}{60} = \frac{3}{60} = \frac{1}{20}
of the tank per minute.
∴ Time taken by the two taps together to empty the tank = 20 minutes.
Hence option [B] is the right answer.

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