Speed in still water is x km/h and that of the stream is y km/h. A man rows a certain distance up and down the stream. What is the average speed for the journey?

Correct option is D

Given: Speed in still water = x km/h, Speed of the stream = y km/h
Formula Used: Average speed = (2 × speed downstream × speed upstream) / (speed downstream + speed upstream)
Solution:
Speed downstream = (x + y) km/h
Speed upstream = (x - y) km/h
Average speed = [2 × (x + y) × (x - y)] / [(x + y) + (x - y)]
= [2 × (x² - y²)] / [2x]
= (x² - y²) / x