Question

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?

• A. $20\frac{1}{2}$days
• B. $20\frac{3}{5}$days
• C. 21 days
• D. $20\frac{4}{7}$days

Answer 1

Answer: (D)

$20\frac{4}{7}$days

8 men working for 9 hours a day can complete a piece of work in 20 days
8 men working for 1 hour a day can complete the work in (20 x 9) days (Less hours, More days)
1 man working for 1 hour a day can complete the work in (20 x 9 x 8) days (Less men, more days)

1 man working for 10 hours a day can complete the work in $\left(\frac{20\times 9\times 8}{10}\right)$ days

7 men working for 10 hours a day can complete the work in $\left(\frac{20\times 9\times 8}{7\times 10}\right)$ days = $\frac{144}{7}$ days = $20\frac{4}{7}$ days