Speed of a man is $12 \text{ km/h}$ in still water. If the rate of current is $4 \text{ km/h}$,then the effective speed of the man upstream is ......... $\text{km/h}$.

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?

$A$ person can row with the stream at $8 \text{ km/h}$ and against the stream at $4 \text{ km/h}$. The speed of the current is (in $\text{km/h}$):

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

$A$ boat travels upstream from $B$ to $A$ and downstream from $A$ to $B$ in $3$ $hours$. If the speed of the boat in still water is $9\, km/h$ and the speed of the current is $3\, km/h$,the distance between $A$ and $B$ is........$km$.

$A, B$ 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?