If the speed of a boat in still water is $20\, km/hr$ and the speed of the current is $5\, km/hr$,then the time taken by the boat to travel $100\, km$ with the current is......$hours$.

$A$ boat moves downstream at the rate of $1 \, km$ in $7 \frac{1}{2} \, \text{minutes}$ and upstream at the rate of $5 \, km/h$. What is the speed (in $km/h$) of the boat in still water?

$A$ boatman can row $2\, km$ against the stream in $20\, minutes$ and return in $18\, minutes.$ Find the rate of the current in $km/h$.

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 ......... $\text{km/h}$.

$A$ boat goes $24 \, km$ upstream and $28 \, km$ downstream in $6 \, hours$. It goes $30 \, km$ upstream and $21 \, km$ downstream in $6 \, hours$ and $30 \, minutes$. The speed of the boat in still water is $...... \, km/hr$.

The speed of a boat in still water is $6\, km/hr$ and the speed of the stream is $1.5\, km/hr$. $A$ man rows to a place at a distance of $22.5\, km$ and comes back to the starting point. The total time taken by him is