Question

A man can row a boat at the rate of $4$km/hr in still water. He takes thrice as much time in going $30$km upstream as in going $30$ km downstream. Find the speed of the stream.

Answer 1

Let the speed of stream be $x$

Now, we know that $time=\frac{D}{speed}$

Now, time taken upstream is $\frac{30}{4-x}$

time taken downstream is $\frac{30}{4+x}$

Now, According to Question

$3\ast \left(\frac{30}{4+x}\right)=\frac{30}{4-x}\Rightarrow 12-3x=4+x\Rightarrow 8=4x\Rightarrow x=2km/hr$