Boat and Stream

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if the speed of a boat in still water is u km/h & the speed of the streams of v km/h than-
speed towards downstream- $(u+v) km/h$
Speed towards up stream- $(u-v) km/h$
if the speed of boat in downstream u km/h and in upstream v km/h
than speed in still water-$\frac{1}{2}(u+v) km/h$
rate or speed of stream=$\frac{1}{2}(a-b) km/h$