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Making the Average Puzzle - Solution
The Puzzle:
If I drive half-way to the city at 30 km/hour, how fast do I have to go for the rest of the way to make the average speed for the entire journey of 60 km/hour?
Our Solution:
You should be there already!
You are half way there, and want to double your average, so your speed would have to be infinite.
Example: Let's say it is 120 km to the city
You get halfway (60 km) at 30 km/h, which takes 2 hours.
To make it all the way (120 km) at 60 km/h would take 2 hours ... but you have already been driving for 2 hours, so your time is up.