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Puzzle Details

Traffic was bad going to work this morning. I only managed to average 30 mph.

How fast must I go home tonight, along the same route, to average 60 mph for the entire round trip?

[Ref: ZNID]

It does not matter how far the trip is, let's assume that it is random distance, say 60 miles, and remembering that Time = Distance ÷ Speed.

The morning trip took 60 miles ÷ 30 mph = 2 hours.

To average the required 60 mph, we would have to travel the total distance (of 120 miles) in 2 hours. However, we've already used all of the two hours for the morning trip!

Choosing any random distance would also show that it can't be done.

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