Time & Work / Pipes & Cisterns

JKSSB Junior Engineer (Mechanical) · Mathematics · 53 practice questions with answers and explanations: 14 Easy, 38 Medium, 1 Hard.

Sample questions

Sample Easy question 1

If 8 workers can complete a wall in 12 days, how many days will 12 workers take?

  1. 7 days
  2. 6 days
  3. 9 days
  4. 8 days
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Answer: D. Total man-days = 8×12 = 96. For 12 workers: 96/12 = 8 days.

Sample Easy question 2

A, B and C can complete a job in 10, 15 and 30 days respectively. If they all work together, in how many days will the job be completed?

  1. 7 days
  2. 4 days
  3. 5 days
  4. 6 days
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Answer: C. Combined rate = 1/10 + 1/15 + 1/30 = 3/30 + 2/30 + 1/30 = 6/30 = 1/5, so together they take 5 days.

Sample Easy question 3

A is 50% more efficient than B. If B alone completes a job in 18 days, in how many days will A alone complete it?

  1. 10 days
  2. 11 days
  3. 13 days
  4. 12 days
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Answer: D. A's efficiency = 1.5 × B's efficiency. Time is inversely proportional to efficiency: A's time = 18/1.5 = 12 days.

Sample Medium question 4

A pipe can fill a tank in 6 hours, and another pipe can empty it in 8 hours. If both are opened together, how long will it take to fill the tank?

  1. 22 hours
  2. 20 hours
  3. 24 hours
  4. 26 hours
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Answer: C. Net rate = 1/6 - 1/8 = 4/24 - 3/24 = 1/24, so the tank fills in 24 hours.

Sample Medium question 5

A and B are twice as efficient as C. If A and B together complete a job in 6 days, how many days will C alone take?

  1. 24 days
  2. 22 days
  3. 20 days
  4. 26 days
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Answer: A. A and B together (twice C's efficiency) do in 6 days what C alone would do in 6×4=24 days (since together they're 4 times as efficient as C alone, being twice-efficient-each with two workers).

Sample Medium question 6

A does twice the work of B in the same time. If B alone can complete a job in 24 days, in how many days can A and B together complete it?

  1. 7 days
  2. 8 days
  3. 9 days
  4. 6 days
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Answer: B. A's rate = 2 × B's rate = 2/24 = 1/12. Combined rate = 1/12 + 1/24 = 2/24+1/24 = 3/24 = 1/8, so together they take 8 days.

Sample Hard question 7

Together, A and B take 18 days to finish a job; A does half as much work as B in three-fourths of B's time. Find B's time alone.

  1. 25
  2. 30
  3. 28
  4. 32
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Answer: B. Working through the ratio gives A's rate as 2/(3x) where x is B's time; solving the combined rate equation gives x = 30 days.

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