Math & Logic · Ages 12–15
Riddle #155
You drive 60 km to the next town at a steady 60 km/h, then drive the same 60 km home at a steady 30 km/h. What is your average speed for the round trip?
You solved this one before
Answer: 40 km/h
The trip out takes 1 hour and the trip back takes 2 — 120 km in 3 hours. Averaging the two speeds (45) is the trap: you spend twice as long travelling at the slower one.