$A$ man can row at the rate of $4 \text{ km/hr}$ in still water. If the time taken to row a certain distance upstream is $3$ times as much as to row the same distance downstream,find the speed of the current in $\text{km/hr}$.

In a river,the ratio of the speed of the stream to the speed of a boat in still water is $2:5$. In another case,the ratio of the speed of the stream to the speed of a boat in still water is $3:4$. What is the ratio of the speeds of the first boat to the second boat in still water?

From the given statements,decide which of the statement$(s)$ is/are necessary to answer the question.
What is the speed of a train?
$I.$ The length of the train is $240 \ m$.
$II.$ The train crosses a pole in $24 \ s$.
$III.$ The train crosses a platform in $48 \ s$.

$A$ man can row $30 \text{ km}$ upstream and $44 \text{ km}$ downstream in $10 \text{ hours}$. Also,he can row $40 \text{ km}$ upstream and $55 \text{ km}$ downstream in $13 \text{ hours}$. Find the rate of the current and the speed of the man in still water (in $\text{km/h}$).

$A$ boatman can row $48\, km$ downstream in $4\, hours$. If the speed of the current is $5\, km/h$,then find in what time will he be able to cover $8\, km$ upstream? (in $hours$)

$A$ man takes twice as long to row a distance against the stream as to row the same distance in favour of the stream. The ratio of the speed of the boat (in still water) and the stream is: