Question

A man can row 5km/h in still water. If the speed of the current is 1km/hr, it takes 3h more in upstream than in the downstream for the same distance. The distance is
A. 36km
B. 24km
C. 20km
D. 32km

Answer 1

Hint- In order to find the distance first we will determine the speed of the man in upstream and downstream with the help of given data, then we will proceed further by using the given statement condition.

Complete step-by-step solution-
Let the distance be =$d$
Speed of man in upstream = 5 – 1 = 4km/h
Speed of man in downstream = 5+1 = 6km/h
According to the question,
Time taken by man in upstream = time taken by man downstream + 3
$
  \dfrac{d}{4} = \dfrac{d}{6} + 3{\text{ }}\left[ {\because {\text{ speed = }}\dfrac{{{\text{distance}}}}{{{\text{time}}}}{\text{ or time = }}\dfrac{{{\text{distance}}}}{{{\text{speed}}}}} \right] \\
  \dfrac{d}{4} - \dfrac{d}{6} = 3 \\
  \dfrac{{3d - 2d}}{{12}} = 3 \\
  d = 36km \\
$
Hence, the correct option is A.

Note- When a man rows in the same direction as the current, we say that it is travelling downstream. When a man rows against the current, it travels upstream. While going upstream current opposes the speed of the man and while moving downstream the current supports the speed of the man.