If a boat goes upstream at a speed of $21\, km/h$ and comes back the same distance at $28\, km/h$,what is the average speed (in $km/h$) for the total journey?

$A$ boat covers a certain distance downstream in $1 \text{ hour}$,while it comes back in $1.5 \text{ hours}$. If the speed of the stream is $3 \text{ km/hr}$,what is the speed of the boat in still water? (in $\text{km/hr}$)

$A$ man can row $44 \text{ km}$ downstream in $4 \text{ hours}$. If the man's rowing rate in still water is $8 \text{ km/hr}$,then find in what time will he cover $25 \text{ km}$ upstream? (in $\text{hours}$)

$A, B$ 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?

The speed of a boat in still water is $10\, km/hr$. If it can travel $26\, km$ downstream and $14\, km$ upstream in the same time,the speed of the stream is.....$km/hr$.

The speed of a boat in still water is $6\, km/h$. It takes the boat twice as long to row up as to row down the river. Find the rate of the stream (in $km/h$).