Multiple choice

Two pipes A and B can fill a tank in 20 hrs and 30 hrs respectively. If both the pipes are opened simultaneously, how much time will be taken to fill the tank?

  1. $12$
  2. $\dfrac { 1 }{ 12 }$
  3. $13$
  4. $\dfrac { 1 }{ 13 }$
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A Correct answer
Explanation

Combined rate = 1/20 + 1/30 = 3/60 + 2/60 = 5/60 = 1/12. Time taken = 12 hours.

AI explanation

Using the least common multiple method, assume the tank's capacity is 60 units since the times are 20 and 30 hours. Pipe A fills at 60 / 20 = 3 units per hour, and pipe B fills at 60 / 30 = 2 units per hour. Their combined rate is 3 + 2 = 5 units per hour, so the total time to fill the 60-unit tank is 60 / 5 = 12 hours.

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