1. In water, the direction along the stream is called downstream. And the direction against the stream is called upstream.
2. Let the speed of a boat in still water be u km/hr and the speed of the stream be v km/hr, then
Speed downstream = (u + v) km/hr
Speed upstream = (u - v) km/hr.
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
Some more shortcut methods
4. Assume that a man can row at the speed of xx km/hr in still water and he rows the same distance up and down in a stream which flows at a rate of yy km/hr. Then his average speed throughout the journey
Speed downstream * Speed upstream/Speed in still water = (x+y)(x-y)/x km/hr
5. Let the speed of a man in still water be x km/hr and the speed of a stream be y km/hr. If he takes t hours more in upstream than to go downstream for the same distance, the distance = (x2 - y2)t/2y km
6. A man rows a certain distance downstream in t1 hours and returns the same distance upstream in t2 hours. If the speed of the stream is y km/hr, then the speed of the man in still water = y [(t2 + t1)/(t2 - t1)] km/hr
7. A man can row a boat in still water at x km/hr in a stream flowing at y km/hr. If it takes him tt hours to row a place and come back, then the distance between the two places
t(x2 - y2)/2x km
8. A man takes n times as long to row upstream as to row downstream the river. If the speed of the man is x km/hr and the speed of the stream is y km/hr, then
x = y(n+1/n-1)
https://gyangossip.com/quantitative-aptitude/mock-test/T4716