$A$ swimmer covers a distance of $28\, km$ against the current and $40\, km$ in the direction of the current. If in each case he takes $4\, hours$,then the speed of the current is..........$km/h$.

$A, B$ and $C$ are situated on the bank of a river which is flowing at a constant rate. $B$ is at an equal distance from $A$ and $C$. $A$ swimmer Avinash takes $10 \, h$ to swim from $A$ to $B$ and $B$ to $A$. Also,he takes $8 \, h$ to swim from $A$ to $C$ in downstream. What is the ratio of the speed of Avinash in still water to the speed of the stream?

$A$ sailor goes $12$ $km$ downstream in $48$ $min$ and returns in $1$ $h$ $20$ $min.$ The speed of the sailor in still water is..........$km/h$.

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:

$A$ man can row at the rate of $3.5 \, km/h$ in still water. If the time taken to row a certain distance upstream is $2 \frac{1}{2}$ times as much as the time taken to row the same distance downstream,find the speed of the current in $km/h$.

The speed of a boat in still water is $7\, km/h$. If its speed in downstream is $10\, km/h$,then the speed of the stream is .......... $km/h$.