Khan/khan-exercises — pull request #15028 by smenks13 (2012-02-29 21:08:36+00:00)
Title: New exercise: Z-scores 1

I thought it might be better to start from the ground up in covering z-scores, so I closed the other pull request and added this more introductory one. I took the problem from this video and randomized it a bit: http://www.khanacademy.org/math/statistics/v/ck12-org-normal-distribution-problems--z-score