Multiple choice

If 20 men working 7 hours a day can do a piece of work in 10 days, in how many days will 15 men working 8 hours a day do the same piece of work ?

  1. $\displaystyle 15\frac{5}{21}$
  2. $\displaystyle 11\frac{2}{3}$
  3. $\displaystyle 6\frac{9}{16}$
  4. $\displaystyle 4\frac{1}{5}$
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B Correct answer
Explanation

Use the formula (M1*D1*H1) = (M2*D2*H2). (20 * 10 * 7) = (15 * D2 * 8). 1400 = 120 * D2. D2 = 1400 / 120 = 140 / 12 = 35 / 3 = 11 2/3 days.

AI explanation

Using the man-days formula of M1 times D1 times H1 equals M2 times D2 times H2, we can equate the total man-hours required for the job. Here, 20 men times 10 days times 7 hours equals 15 men times the unknown days times 8 hours. This gives 1400 equals 120 times the unknown days. Dividing 1400 by 120 yields 140 divided by 12, which is 35 divided by 3 days. This gives 11 and 2/3 days.

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