The speed of a boat downstream is 15 km/hr and the speed of the stream is 1.5 km/hr. The speed of the boat upstream is?

Speed of current = 5 - 3.5 = 1.5 km/hr.
So the speed of man along the current = 5 + 1.5 = 6.5 km/hr

Let the rate against the current be x km/hr.
Then, (12 - x) / 2 = 1.5
? 12 - x = 3
? x = 9 km/hr

Speed upstream = (40/8) km/hr = 5 km/hr
Speed downstream = (36/6) km/hr = 6 km/hr

Speed of boat in still water = (5 + 6)/2 km/hr = 5.5 km/hr.

Let the speed of the stream = x km/h
?Speed of boat in still water = 10 km/h
Speed of boat downstream = ( x + 10) km/h
Speed of boat upstream=(10 - x) km/h

? Time taken to travel 26 km downstream=[ 26 / ( 10 + x ) ] h
Time taken to travel 14 km upstream=[ 14 /( 10 - x )] h
? By condition [ 26 / ( 10 + x)]=[ 14 / ( 10 - x)]
? 26(10-x)=14(10+x)

? 260-26x =140 + 14x
? 40x=120
? x = 3 Here, speed of stream = 3 km/h

Rate in still water=[(1/2)(u+v)] km/h
Rate of current=[(1/2)(u-v)] km/h
where u= speed of boat in downstream
v=speed of boat in upstream

Speed of boat in still water=[(1/2)(7+13)] =10 km/h
Speed of the stream =[(1/2)(13-7)]=3 km/h

Let the speed of stream be x km/hr
Then, speed upstream = (2 - x ) km/hr
? 2 - x = 1
? x = 1 km/hr

Man's rate in still water = (14 + 9)/2 km/hr = 11.5 km/hr

Speed of stream = (11 - 8)/2 km/hr = 1.5 km/hr

Speed in upstream = Speed in still water - Speed of stream.
? 1 = 2 - x
? x = 2 - 1 = 1 km/hr

? Speed upstream = 14 x (60/56) = 15 km/hr
Speed in upstream = Speed in still water - Speed of stream.
? x - 2 = 15
? x = 17 km/hr