A mathematician’s Advent Calendar

 

Yes, this is from xkcd.  How did you guess?

 

http://xkcd.com/994/ 

If you don’t get the joke: http://www.answers.com/topic/zeno-s-paradoxes 

Achilles runs a race with a tortoise, who has a start of n metres. Suppose the tortoise runs one-tenth as fast as Achilles. Then by the time Achilles has reached the tortoise's starting-point, the tortoise is n/10 metres ahead. By the time Achilles has reached that point, the tortoise is n/100 metres ahead, and so on ad infinitum. So Achilles cannot catch the tortoise.
Read more: http://www.answers.com/topic/zeno-s-paradoxes#ixzz1hNfGUQrp