A certain number of men can finish a piece of work in 100 days. If there were 10 men less, it would take 10 days more for the work to be finished. How many men were there originally?
Answer: D
The total work in man-days is fixed.
\[ 100M = 110(M - 10) \]
\[ 100M = 110M - 1100 \quad\Longrightarrow\quad 10M = 1100 \]
\[ M = 110 \]
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A man can walk a certain distance at a uniform speed in 100 days. How long will it take him to cover twice the distance at half the normal speed?
Answer: E
Time is proportional to distance and inversely proportional to speed.
\[ t' = 100 \times 2 \times \frac{1}{1/2} = 100 \times 2 \times 2 \]
\[ = 400 \text{ days} \]
Doubling the distance doubles the time, and halving the speed doubles it again - the two effects compound.
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