Discussion

A man can row a boat at 20 kmph in still water. If the speed of the stream is 6 kmph, what is the time taken to row a distance of 60 km downstream?

Answer: D

With \( b \) the still-water speed and \( r \) the stream's,

\[ \text{downstream} = b + r, \qquad \text{upstream} = b - r \]

\[ b + r = 20 + 6 = 26 \text{ kmph} \]

\[ t = \frac{60}{26} = \frac{30}{13} \text{ hours} \]

That is about 2 hours 18 minutes. Using the still-water speed would give 3 hours - the current is helping, so the trip must be faster than that.

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