Question

Sixty-four men working 8 hours a day plan to complete a piece of work in 9 days. However, 5 days later they found that they had completed only 40% of the work. They now wanted to finish the remaining portion of the work in 4 more days. How many hours per day do they need to work in order to achieve the target?

• A. 11
• B. 12
• C. 13
• D. 15

Answer 1

The correct option is D 15

Total work (in terms of man-hours) = $\frac{64\times 8\times 5}{0.4}$
Work remaining (in terms of man-hours) = $\frac{64\times 8\times 5}{0.4}\times 0.6$
Working hours per day needed to complete remaining work in 4 days
= $\frac{64\times 8\times 5}{0.4}\times 0.6\times \frac{1}{64\times 4}$
= 15 hours.

Alternate Approach:
$\begin{array}{cccc}Men& WorkingHours& Day& Workdone\\ 64& 8& 5& 40\%\\ 64& n\left(say\right)& 4& 60\%\end{array}$
40% work in 40 hours $\to$ 60% work in 60 hours.
Hence, working hours
$=\frac{60}{4}=15hours$