Multiple choice general knowledge math & puzzles

Thirty men take 20 days to omplete a job working 9 hours a day.How many hour a day should 40 men work to complete the job?

  1. 8 hrs

  2. 7 1/2 hrs

  3. 7 hrs

  4. 9 hrs

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Total work = 30 men × 20 days × 9 hours/day = 5400 man-hours. This work must be completed by 40 men in 20 days. Hours per day = 5400/(40×20) = 6.75 hours = 7.5 hours. Work done is inversely proportional to men when days are fixed.