A man can row upstream at 10 Km/hr and downstream at 18 Km/hr. Find the man's rate in still water?

14 Km/hr

Let,

Speed of boat in still water= x

Speed of stream/current = y

According to the question:

Upstream speed (Us) = 10 km/h i.e. x - y = 10 km/h -----1st equation

Downstream speed (Ds) = 18 km/h i.e. x + y = 18 km/h -----2nd equation

Man's speed rate in still water means we have to find x

So, add the both equations:

x - y + x + y = 10 + 18

2x = 28

x = 14 km/hr