Discussion
A man can row 6 kmph in still water. When the river is running at 1.2 kmph, it takes him 1 hour to row to a place and back. What is the total distance travelled by the man?
Answer: C
With \( b \) the still-water speed and \( r \) the stream's,
\[ \text{downstream} = b + r, \qquad \text{upstream} = b - r \]
\[ b + r = 7.2 \text{ kmph}, \qquad b - r = 4.8 \text{ kmph} \]
\[ \frac{D}{7.2} + \frac{D}{4.8} = 1 \quad\Longrightarrow\quad \frac{5D}{14.4} = 1 \quad\Longrightarrow\quad D = 2.88 \text{ km} \]
That is the one-way distance. The question asks for the total journey, so it must be doubled:
\[ 2 \times 2.88 = 5.76 \text{ km} \]
2.88 km is the correct answer to a different question - how far away the place is.
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