A man takes twice as long to row up as to row down the river. If the rate of river is 4km/hr.find the rate of the man in still water
Speed of the boat in still water =9 km
Let D be the distance. It takes him twice the time to row upstream compared to downstream.
Let speed of the current be x kmph
Speed downstream =(9+x)
Speed upstream = (9-x)
Ratio of time taken for upstream to time taken for downstream = D/(9-x) ÷ D/(9+x) =1/2
2 (9 - x)= 9+x
18 -2x = 9+x
-3x =-9 hence x = 3
Rate of stream = 3 kmph.