Question

In still water, the boat rows 9 km, whereas while going upstream the boat takes thrice the time to cover the same distance. The speed of the current is (in km/hr) ______

Answer 1

Suppose in still water the boat takes 1 hour to cover 9 km.
So in upstream, time taken to move 9 km = 3 hours

In 1 hour, the boat covers $\frac{9}{3}=3$ km upstream
So, upstream speed = 3 km/hr

$\therefore$ Speed of the boat - speed of the current = 3 km/hr

But, the speed of the boat is 9 km/hr

Therefore speed of the stream = 9 - 3 = 6 km/hr.