Multiple choice

Three pipes X, Y and Z can fill a water cooler in 4 hours, 2 hours and 12 hours respectively. How many hours will it take to fill the water cooler if all the pipes are used?

  1. 0.5 hour

  2. 1 hour

  3. 1.2 hours

  4. 2 hours
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The rates of the pipes are 1/4, 1/2, and 1/12 of the cooler per hour. Summing these gives (3/12 + 6/12 + 1/12) = 10/12 = 5/6 of the cooler per hour. The time taken is the reciprocal, 6/5 = 1.2 hours.

AI explanation

Using the formula for combined work, the part of the cooler filled in one hour by all three pipes is the sum of their individual rates, giving 1/4 + 1/2 + 1/12. Finding a common denominator yields 3/12 + 6/12 + 1/12 = 10/12, which simplifies to 5/6. The total time to fill the cooler is the reciprocal of this combined rate, so the tank fills in 6/5 hours, making the time 1.2 hours.

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