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 swim in still water at $4 \, km/h$. If the speed of the water current is $2 \, km/h$,how many hours will the man take to swim back against the current for $6 \, km$?

$A$ man takes $3$ $hours$ $45$ $minutes$ to row a boat $15 \; km$ downstream of a river and $2$ $hours$ $30$ $minutes$ to cover a distance of $5 \; km$ upstream. Find the speed of the river current in $km/hr$.

$A$ man can row $6\, km/h$ in still water. If the speed of the current is $2\, km/h$,it takes $3\, hours$ more in upstream than in the downstream for the same distance. The distance is.....$km$.

$A$ boat goes $14 \ km$ upstream in $42 \ minutes$. The speed of the stream is $4 \ km$. The speed of the boat in still water 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?