Question

A boat takes 30 minutes less to travel 36
kms downstream than when travelling
upstream. If the speed of the current of
the stream is 3kmph find the speed of
the boat in still water.​

Answer 1

Answer:

Let the speed of the stream be x km/hr.

Speed of boat in still water =10 km/hr

∴ Speed of boat downstream =(10+x) km/hr

Speed of boat upstream =(10−x) km/hr

Given, (10−x)36−(10+x)36=6090

⇒(10−x)(10+x)36(10+x)−36(10−x)=23

⇒100−x272x=23    

⇒    144x=300−3 x2

⇒3x2+144x−300=0

⇒3x2+150x−6x−300=0

⇒3x(x+50)−6(x+50)=0

⇒(3x−6)(x+50)=0

⇒ x=2 or x=−50

Since speed is not negative, x=2 km/hr.