Need quick apache help

For some reason, I forgot how to do this with mod_rewrite.

Okay. I have a bunch of files like this:

http://www.example.com/200.php
http://www.example.com/300.php
http://www.example.com/400.php

So on and so forth. But, I only want people to type in:

http://www.example.com/200

and it will redirect them to:

http://www.example.com/200.php

I cannot use Redirect 301's, I can only use mod_rewrite

Any help?