This article is from the Puzzles FAQ, by Chris Cole email@example.com and Matthew Daly firstname.lastname@example.org with numerous contributions by others.
"This is a quiz written by Einstein in the last century. He said that 98%
of the world's population could not solve it...." This is followed by a
series of fifteen clues about five European men who live in houses of
different houses, drink different beverages, smoke different cigarettes,
and keep different pets. Who keeps the fish?
The German keeps the fish. A detailed explanation is available at
http://www.frontiernet.net/~mwdaly/recpuzzles/einstein.html. For the
record, Einstein didn't write the puzzle and far more than 2% of the
world's population could solve it.