Mixed workforce rates: 8 men finish the job in 12 days; 4 women finish it in 48 days; 10 children finish it in 24 days. In how many days will 10 men, 4 women, and 10 children working together complete the same job?

Difficulty: Medium

Correct Answer: 6 days

Explanation:


Introduction / Context:
Different categories of workers often have different speeds. Convert each category to a per-person daily rate, add rates to get a team rate, and then compute time = work / rate. The unitary-method approach keeps the arithmetic clean and scalable.


Given Data / Assumptions:

  • 8 men complete in 12 days ⇒ 1 man's rate = 1 / (8*12) = 1/96 job/day.
  • 4 women complete in 48 days ⇒ 1 woman's rate = 1 / (4*48) = 1/192 job/day.
  • 10 children complete in 24 days ⇒ 1 child's rate = 1 / (10*24) = 1/240 job/day.
  • Team: 10 men + 4 women + 10 children.


Concept / Approach:
Team rate = sum of individual rates, then time = 1 / (team rate). Be precise with fractions to avoid compounding rounding errors.


Step-by-Step Solution:

Men: 10 * (1/96) = 10/96 = 5/48 Women: 4 * (1/192) = 4/192 = 1/48 Children: 10 * (1/240) = 1/24 Team rate = 5/48 + 1/48 + 1/24 = 6/48 + 2/48 = 8/48 = 1/6 job/day Time = 1 / (1/6) = 6 days


Verification / Alternative check:
Since the combined rate is exactly 1/6 job/day, finishing in 6 days is exact (no rounding).


Why Other Options Are Wrong:
5, 7, 8, 10 days contradict the exact combined-rate computation 1/6 job/day.


Common Pitfalls:
Adding times instead of rates, or using proportional reasoning on days rather than on daily work rates leads to wrong results.


Final Answer:
6 days

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