$A$ boatman goes $2\, km$ against the stream in $1\, hour$ and goes $1\, km$ along the current in $10\, minutes.$ How long will he take to go $5\, km$ in stationary water?

Twice the speed downstream is equal to thrice the speed upstream. The ratio of the speed in still water to the speed of the current is:

$A$ river is flowing at a speed of $5\, km/h$ in a particular direction. $A$ man,who can swim at a speed of $20\, km/h$ in still water,starts swimming along the direction of flow of the river from point $A$ and reaches another point $B$ which is at a distance of $30\, km$ from the starting point $A$. On reaching point $B$,the man turns back and starts swimming against the direction of flow of the river and stops after reaching point $A$. The total time taken by the man to complete his journey is:

$A$ man can row $18 \ km/h$ in still water. It takes him thrice as long to row up as to row down the river. Find the rate of the stream. (in $km/h$)

$A$ man can row $15\, km$ downstream in $3\, hours$ and $5\, km$ upstream in $2.5\, hours$. His speed in still water in $(km/hr)$ is:

$A$ man rows at $9 \frac{1}{3} \text{ km/h}$ in still water and finds that it takes him thrice as much time to row up than to row down the same distance in the river. The speed of the current is.......$\text{km/h}$