This article is from the Puzzles FAQ, by Chris Cole firstname.lastname@example.org and Matthew Daly email@example.com with numerous contributions by others.
==> unexpected <== [logic/part5]
Swedish civil defense authorities announced that a civil defense drill
would be held one day the following week, but the actual day would be a
==> envelope <== [logic/part5]
Someone has prepared two envelopes containing money. One contains twice as
much money as the other. You have decided to pick one envelope, but you
can then "prove" that the other envelope contains more money than the one
Threads about these and other logical paradoxes tend to go on for a long
time and can get nasty as people try to convince each other of the truth
of their positions. If you would like to start a thread about a paradox,
please read the archive explanation first to see if that clears things up
for you. Whether you are reading or posting to one of these threads,
remember that there are many logical interpretations that are often
equally valid. If there weren't, it wouldn't be a paradox, would it?