>> Well if the mean is 60 and the standard deviation is 13, one standard
deviation below the mean would be 60 minus 13. 60 minus 13 is 47. So here's 60,
the mean, and we go back 13, and this value is 47. Two standard deviations above
the mean would be 86, because we go up 13 for one standard deviation and another
13 for two standard deviations. And finally, the mean minus two standard
deviations would be 60 minus 13 minus 13, which is 34.