$A$ 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 $km/h$).

$A$ boatman rows $1\, km$ in $5\, min$ along the stream and $6\, km$ in $1\, h$ against the stream. The speed of the stream is in $km/h$:

$A$ man swims downstream a distance of $15\, km$ in $1\, h$. If the speed of the current is $5\, km/h$,the time taken by the man to swim the same distance upstream is

$A$ man can row upstream $36 \text{ km}$ in $6 \text{ hours}$. If the speed of a man in still water is $8 \text{ km/hr}$,find how much distance he can cover downstream in $10 \text{ hours}$? (in $\text{km}$)

$A$ motor boat,whose speed is $15 \text{ km/hr}$ in still water,goes $30 \text{ km}$ downstream and comes back in a total of $4 \text{ hours } 30 \text{ minutes}$. The speed of the stream (in $\text{km/hr}$) is:

There is a road beside a river. Two friends started from a place $A,$ moved to a temple situated at another place $B$ and then returned to $A$ again. One of them moves on a cycle at a speed of $12\, km/hr,$ while the other sails on a boat at a speed of $10\, km/hr.$ If the river flows at the speed of $4\, km/hr,$ which of the two friends will return to place $A$ first?