Multiple choice

8 men working for 9 hours a day can complete a piece of work in 20 days. In how many days can 7 men working for 10 hours a day complete the same piece of work?

  1. $\displaystyle 20\frac{1}{2}$days
  2. $\displaystyle 20\frac{3}{5}$days

  3. 21 days
  4. $\displaystyle 20\frac{4}{7}$days
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Total work = 8 * 9 * 20 = 1440 man-hours. New setup: 7 men * 10 hours * D days = 1440. D = 1440 / 70 = 144 / 7 = 20 and 4/7 days.

AI explanation

Using the formula M1 times D1 times H1 equals M2 times D2 times H2, we can equate the total man-hours needed for the work. Substituting the given values, 8 men times 20 days times 9 hours equals 7 men times the unknown days times 10 hours. This gives 1440 equals 70 times the unknown days. Dividing 1440 by 70 gives 144/7 days, which mixed fraction form is 20 and 4/7 days.

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