Question

A man rowing at the rate of 5 km an hour in still water takes thrice as much time in going 40 km up the river as in going 40 km down. Find the rate at which the river flows.

Answer 1

Speed of the boat in water =5 km/hr

Let the speed of the stream be x km/hr

So, the speed of the boat upstream will be
(5-x) km / hr

So, the speed of the boat downstream is (5+x)
k/hr

Time given to cover 40 km upstream = 3(time
taken to cover dowmstream)

⇒40/ (5-x) km/hr = 3(5+x)

⇒1/(5-x)=3(5+x)

⇒5+x=15-3x

⇒x+3x=15-5

⇒4x=10

⇒X=10/4

⇒X=5/2

∴x=2.5 km/hr