Multiple choice

Pipe A can fill an empty tank in 5 hours and pipe B takes 6.25 hours to fill it. When the tank was empty, both pipes were opened together, but after some time, pipe B was closed, which took 3.4 hours to fill the tank. For how many hours was pipe B opened?

  1. 2

  2. 1

  3. 2.5

  4. 1.5
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Pipe A fills at 1/5 tank per hour. Pipe B fills at 1/6.25 = 4/25 tank per hour. Combined rate = 1/5 + 4/25 = 9/25 per hour. Let both pipes be open for t hours. Then A alone works for (3.4 - t) hours. Equation: (9/25)t + (1/5)(3.4 - t) = 1. Solving: (4/25)t = 0.32, so t = 2 hours. Option A is correct.

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