Multiple choice

Arlo works with a water supply corporation. Due to a power cut in an area, the corporation has to send a water tank in order to fulfill the residents' water needs. So, Arlo puts five inlet pipes in the tank in order to fill it with water. Out of the five pipes, three have narrow openings and two have wide openings. The rate at which the narrow pipes work is half the rate of the pipes with wide openings. If all the pipes work together, then they will take what fraction of the time taken by the two wide pipes working together to fill the tank?

  1. 4 7

  2. 3 7

  3. 7 4

  4. 7 3

  5. 2 7
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Let each wide pipe fill at rate 2r and each narrow pipe at rate r. All five together fill at 3r + 4r = 7r, while the two wide pipes fill at 4r. The ratio of times is (1/7r)/(1/4r) = 4/7. Option A is meant to represent 4/7.

AI explanation

Let the rate of a wide pipe be 2 units per hour, so a narrow pipe has a rate of 1 unit per hour, making the two wide pipes together fill at 4 units per hour. The five pipes working together have a combined rate of 2(2) + 3(1) = 7 units per hour. Because work is the product of rate and time, the time taken is inversely proportional to the rate, so the ratio of the time taken by all five pipes to the time taken by the two wide pipes is 4/7. The required fraction of the time is 4/7.

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