Multiple choice

Pipe A and B running together can fill a cistern in 6 minutes. If B takes 5 minutes more than a to fill the cistern then the time in which A will fill the cistern separately will be -

  1. 15 minutes

  2. 20 minutes

  3. 10 minutes

  4. 25 minutes

  5. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let A's time = t minutes. Then B's time = t + 5. Combined rate: 1/t + 1/(t+5) = 1/6. Solving: (t+5 + t) / t(t+5) = 1/6, giving 6(2t+5) = t(t+5). This leads to 12t + 30 = t² + 5t, or t² - 7t - 30 = 0. Factoring: (t-10)(t+3) = 0, so t = 10. Options A and B are too long. Option D is too long.

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