A boat rows a distance of 12 km downstream at 13 km/h and covers the same distance upstream at 7 km/h. What is the average speed of the boat ?

9.1

The correct answer is option (2) : 9.1 km/h

$u= 13\, km/h$

$v= 7\, km/h$

Speed of boat in still water $x=\frac{13+7}{2}$

$= 10\, km/h$

Average speed $=\frac{u+v}{\text{Speed in still water }}$

$= \frac{13×7}{10}= 9.1\, km/h$