Multiple choice

A water pipe can fill a swimming pool in 12 hours, while another pipe can drain the full pool in 18 hours. If both pipes are opened simultaneously, how long will it take to fill the pool completely?

  1. 24 hours

  2. 36 hours

  3. 48 hours

  4. 72 hours

  5. 108 hours
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The filling pipe fills 1/12 of the pool per hour, and the draining pipe removes 1/18 of the pool per hour. The combined rate is 1/12 - 1/18 = 3/36 - 2/36 = 1/36 of the pool per hour. Thus, it takes 36 hours to fill the pool.

AI explanation

Using the net capacity method, the first pipe fills 1/12 of the pool per hour while the second pipe drains 1/18 per hour. Their combined hourly rate is 1/12 minus 1/18, which equals 1/36. Therefore, the total time taken to fill the pool completely is 36 hours.

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