Question

A motor boat goes 30 km downstream and comes back in 4 h 30 min. If the speed of the stream is 5 km/h, find the speed of the boat in still water.

Answer 1

Let the speed of the stream be x km/hr

Then,

Speed downstream = (15 + x) km/hr

Speed upstream = (15 - x) km/hr

∴3015+x+3015−x=412⇒900225−x2=92⇒9x2=225⇒x2=25⇒x=5km/hr