Binary

Riddle: There are 10 types of people in the world. Who are they?

Answer: Those who understand binary, and those who don't. In Binary 10 is equal to the number two in base ten.

Source: https://www.riddles.com/index.php/5807

There are 10 types of people in the world. Who are they? — Binary by 6085 v1.

Riddle: There are 10 types of people in the world. Who are they? Answer: Those who understand binary, and those who don't. In Binary 10 is equal to the number two in base ten. — by 6085 v2.