**Diophantus of Alexandria**, a Greek mathematician, is considered by many sources to be the “father” of algebra. He is famous for two works, both of which are unfinished. One is about polygonal numbers, while the other more influential work was titled *Arithmetica*, which was the first known book to employ algebra in a modern way. It also inspired the rebirth of number theory.

Not much is known about his life, but we can approximate how old Diophantus lived to be from the following riddle:

**Diophantus’s youth lasted one sixth of his life. He grew a beard after one twelfth more. After one seventh more of his life, he married. Five years later, he and his wife had a son. The son lived exactly one half as long as his father, and Diophantus died four years after his son. **

**How many years did Diophantus live? **(Hint: Set up an algebraic equation equal to his age!)

For the answer to the riddle, click here.

Source (MLA Format): “Diophantus of Alexandria.” *Encyclopædia Britannica. Encyclopædia Britannica Online*. Encyclopædia Britannica Inc., 2012. Web. 20 Feb. 2012. <http://www.britannica.com/EBchecked/topic/164347/Diophantus-of-Alexandria>.