A man rows to a place of 60 km distant and back in 13 hour 30 minutes. He finds that he can row 5 km with the stream in the same time as he can row 4km against the stream. FInd the rate of stream.

 a) 1 km/hr
 b) 1/2 km/hr
 c) 3/2 km/hr
 d) 8 km.hr

SSC CHSL-2015

1 km/hr. Solution Assume that he moves 5 km downstream in t hours. Then, speed downstream = distance/time= 5/t km/hr speed upstream = 4/t km/hr He rows to a place 60 km distant and come back in 13.5 hours (13 hour 30 minute) ==> ==> t = 0.5 Speed downstream = 5/0.5 = 10 km/hr Speed upstream = 4/0.5 = 8 km/hr Speed in still water = (Speed downstream - Speed upstream)/2 = (10-8)/2 = 1 km/hr