Multiple choice

A water tank is filled in 3 hours by 3 pipes P, Q and R working together. The pipe P is 3 times as fast as pipe Q is 4 times as fast as pipe R. Then in how much time will pipe R take to fill the tank alone?

  1. 40 hrs

  2. 51 hrs

  3. 55 hrs

  4. 44 hrs

  5. Can’t determined
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let R's rate = 1 unit tank/hr. Then Q's rate = 4×R = 4 units/hr, and P's rate = 3×Q = 12 units/hr. Combined rate = 1+4+12 = 17 units/hr. Time together = 1/17 hr/tank = 3 hours, so 1 tank = 51 hours. R alone takes 51/1 = 51 hours. Option A (40), C (55), D (44), and E are incorrect.

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