$A$ 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:

$A$ boatman can row $2\, km$ against the stream in $20\, minutes$ and return in $18\, minutes.$ Find the rate of the current in $km/h$.

$A$ motor-boat can travel at $10 \, km/h$ in still water. It travelled $91 \, km$ downstream in a river and then returned to the same place,taking altogether $20 \, hours$. Find the rate of flow of the river (in $km/h$).

$A$ boat can travel with a speed of $13 \text{ km/hr}$ in still water. If the speed of the stream is $4 \text{ km/hr}$,the time taken by the boat to travel $63 \text{ km}$ in the opposite direction (upstream) is........$hrs$.

$A$ man takes $3$ $hours$ $45$ $minutes$ to row a boat $15 \; km$ downstream of a river and $2$ $hours$ $30$ $minutes$ to cover a distance of $5 \; km$ upstream. Find the speed of the river current in $km/hr$.

$A$ man moves $20 \, km$ downstream in $5 \, hours$ and $10 \, km$ upstream in the same time. The speed of the stream is...........$km/h$.