A man goes uphill with an average speed of 24 km/h and comes down with an average speed of 36 km/h. The distance travelled in both cases being the same. The average speed for the entire journey is:

28.8 km/h

Average of speed during uphill (S₁) = 24 kmph

Average of speed during down (S₂) = 36 kmph

Average speed = (2 × S1 × S2)/(S1 + S2)

Average speed = (2 × 24 × 36)/(24 + 36)

⇒ 1728/60 = 28.8 kmph