This article is from the Puzzles FAQ, by Chris Cole chris@questrel.questrel.com and Matthew Daly mwdaly@pobox.com with numerous contributions by others.
Every morning when I warm my milk for breakfast, I put one cup of milk
in the microwave (which is in working order) for exactly 84 seconds. Why?
real-life/microwave.s
When you put your cup in the microwave, the handle on the cup is
pointing towards you. Your microwave has a revolving plate on which the
cup is placed. After 84 seconds, the handle is again in it's initial
position, so you can take the cup out without burning your hands.
 
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