Multiple choice

Three pipes X, Y and Z can fill a tank in 8 hours. Pipe X is thrice as fast as Y and pipe Y is twice as fast as pipe Z. How much time will pipe Z alone take to fill the tank?

  1. 64 hours

  2. 72 hours

  3. 74 hours

  4. 76 hours

  5. 80 hours
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let Z's rate be z. Y = 2z, X = 3Y = 6z. Combined rate = z + 2z + 6z = 9z. 9z = 1/8 (tank per hour). z = 1/72. Z takes 72 hours.

AI explanation

By the ratio of efficiencies, if Z has a speed of x, Y has a speed of 2x, and X has a speed of 6x, making their combined capacity 9x. Their combined time is 8 hours, so their combined rate is 1/8 of the tank per hour, which sets 9x = 1/8 and gives x = 1/72. Since pipe Z alone works at this rate of x per hour, it will take exactly 72 hours to fill the tank.

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