Khan/khan-exercises — pull request #40338 by Pinkerton (2013-02-15 02:08:16+00:00)
Title: New Exercise: Relative and percent error

I made an exercise for practicing relative and percent error. This is a response to [Trello Card #451](https://trello.com/card/relative-percent-error/4d87e664967a0775082939ab/451).

I've tried to make the hints as helpful as possible and keep the experimental value close to the actual value to simulate realistic amounts of error.