Multiple choice

Two pipes individually can fill a tank in 10 hours and 12 hours, while a third pipe can empty the full tank in 20 hours. In how much time will the tank be filled, if all three pipes operate together?

  1. 8 hours

  2. 8 hours and 35 minutes

  3. 7 hours and 35 minutes

  4. 7 hours and 30 minutes

  5. 7 hours and 45 minutes
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Work rate = 1/10 + 1/12 - 1/20 = (6+5-3)/60 = 8/60 = 2/15. Time = 15/2 = 7.5 hours, which is 7 hours and 30 minutes.

AI explanation

Using the net work formula, the combined rate of the three pipes is calculated as one tenth minus one twentieth plus one twelfth, which equals seven sixtieths of the tank per hour. The total time required to fill the tank is the reciprocal of this combined rate, giving 60 divided by 7 hours. Converting this fraction gives exactly 7 hours and 30 minutes.

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