$A$ boat takes $3$ $hours$ to travel from place $M$ to $N$ downstream and back from $N$ to $M$ upstream. If the speed of the boat in still water is $4$ $km/h$,what is the distance between the two places? (in $km$)

$A$ 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

Aditya can row with the stream at $10 \text{ km/h}$ and against the stream at $6 \text{ km/h}$. His speed in still water is .......... $\text{km/h}$.

$A$ man can row $30 \text{ km}$ upstream and $44 \text{ km}$ downstream in $10 \text{ hours}$. Also,he can row $40 \text{ km}$ upstream and $55 \text{ km}$ downstream in $13 \text{ hours}$. Find the rate of the current and the speed of the man in still water.

$A$ man swimming in a stream which flows at $1 \frac{1}{2} \text{ km/h}$ finds that in a given time he can swim twice as far with the stream as he can against it. At what rate does he swim? (in $\text{km/h}$)

Rahul can travel $12 \text{ miles}$ downstream in a certain river in $6 \text{ hours}$ less than it takes him to travel the same distance upstream. But if he could double his usual rowing rate for his $24 \text{ mile}$ round trip,the downstream $12 \text{ miles}$ would take only one hour less than the upstream $12 \text{ miles}$. What is the speed of the current in $\text{miles/hour}$?