1.In water ,the direction along the stream is called downstream and ,the direction against the stream is called upstream.
2.If the speed of a boat in still water is u km/hr and the speed of the stream is v km/hr,then:
3.If the speed downstream is a km/hr and the speed upstream is b km/hr,then :
speed in still water=1/2(a+b)km/hr
rate of stream=1/2(a-b)km/hr