A man travels from $X$ to $Y$ at $30$ km/h and returns at $20$ km/h. His average speed for the whole trip is:

A man travels from $X$ to $Y$ at $30$ km/h and returns at $20$ km/h. His average speed for the whole trip is:
  1. $22$ km/h
  2. $24$ km/h
  3. $25$ km/h
  4. $26$ km/h

Solution

Average for equal distances $= \dfrac{2 \cdot 30 \cdot 20}{30 + 20} = \dfrac{1200}{50} = 24$ km/h.

Asked in: IMO

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