Same job, different crew size: If 36 men can do a piece of work in 25 hours, in how many hours will 15 men do the same work (same rate)?
Aptitude
Unitary Method
Difficulty: Easy
Choose an option
Answer
Correct Answer: 60
Explanation
Introduction / Context:Work done is men * hours for a fixed job. With fewer men, the required hours increase so that the product remains constant. We compute total man-hours and then divide by the new crew size.Given Data / Assumptions:
- 36 men complete in 25 hours.
- New crew: 15 men.
Concept / Approach:Total man-hours = men * hours = constant for the job. So hours2 = (36 * 25) / 15.Step-by-Step Solution:
Total man-hours = 36 * 25 = 900.Hours for 15 men = 900 / 15 = 60 hours.Verification / Alternative check:Proportionality: reducing men by a factor of 36/15 = 2.4 increases time by 2.4; 25 * 2.4 = 60.
Why Other Options Are Wrong:
- 45, 55, 72: Do not preserve the constant 900 man-hours for completion.
Common Pitfalls:Multiplying instead of dividing by the new crew size or mixing units. Keep the men * hours product equal to the known job total.
Final Answer:
60