10 Kinds of People in the World
There are 10 kinds of people in the world — those who understand binary and those who don't.
There are 10 kinds of people in the world — those who understand trinary, those who don't understand trinary and those who mistake it for binary.
Other humor in the GNU Humor Collection.
Disclaimer
The first joke was submitted by Colin Sharpe and the second by François Celliers.
The Free Software Foundation claims no copyright on this joke.