On Friday I posted this puzzle.
You drive to your office at 20 mph and return by the same route at 30 mph. Discounting the time spent at the office, what was your average speed?
If you have not tried to solve it, have a go now. For everyone else the answer is after the break.
The average speed is 24 mph, but can you explain why?
I have produced an ebook containing 101 of the previous Friday Puzzles! It is called PUZZLED and is available for the Kindle (UK here and USA here) and on the iBookstore (UK here in the USA here). You can try 101 of the puzzles for free here.