Question

A man can row a boat at a speed of $\frac{25}{4}$ mph in still water. If he takes 3 times as long to row a distance upstream as to row the same distance downstream, then find the speed of the stream (in mph).

• A. 1.125 mph
• B. 2.125 mph
• C. 4.125 mph
• D. 3.125 mph

Answer 1

The correct option is D 3.125 mph

Let the speed of the stream be 'x' mph.

Speed of the boat upstream = Speed of rowing – Speed of the stream

$\text{Rate upstream}=\frac{25}{4}–x$

Speed of the boat downsteam = Speed of rowing + Speed of the stream

$\text{Rate downstream}=\frac{25}{4}+x$

Let's assume that the time taken in downstream and upstream is 1 hour and 3 hours, respectively.

We know,
Distance = Speed $\times$ Time

$⟹(\frac{25}{4}+x)\times 1=(\frac{25}{4}–x)\times 3$

$⟹25+4x=75–12x$

$⟹12x+4x=75–25$

$⟹16x=50$

$⟹x=3.125$ mph