Multiple choice

If pipes X and Y can fill a tank in 14 minutes and 20 minutes respectively. Both are kept open for 3 minutes and then Y is closed and X fills the rest of the tank in p minutes. For approximately how long was pipe X kept open in all?

  1. 10 minutes

  2. 12 minutes

  3. 9 minutes

  4. 7 minutes

  5. 15 minutes
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Pipe X fills at 1/14 per min, Y at 1/20 per min. In 3 min together: 3(1/14+1/20) = 3(17/140) = 51/140. Remaining: 89/140. X fills this in p minutes: p/14 = 89/140, so p = 8.94 ≈ 9. Total X time = 3+9 = 12 minutes. Answer B (12) is approximately correct.

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