Question

A boat running downstream, covers a distance of 20 km in 2 h, while it covers the same distance upstream in 5 h. then, speed of the boat in still water

Answer 1

Downstream speed = distance/time = 20/2 = 10 kmph
Upstream speed = distance/time = 20/5 = 4 kmph

Let speed of boat in still water = x kmph
Let Speed of stream = y kmph
Down stream speed = x + y
Upstream speed = x - y

10 = x + y
4  = x - y

Add both equations:
14 = 2x
x= 7 kmph
Hence speed of boat in still water = 7 kmph
Hope this helps