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100 points for $49 worth of Veritas practice GMATs FREE VERITAS PRACTICE GMAT EXAMS Earn 10 Points Per Post Earn 10 Points Per Thanks Earn 10 Points Per Upvote ## The age of a group of people follows a distribution, which ##### This topic has 2 expert replies and 0 member replies ### Top Member ## The age of a group of people follows a distribution, which ## Timer 00:00 ## Your Answer A B C D E ## Global Stats Difficult The age of a group of people follows a distribution, which is symmetric about the average (mean) A. If 95% of the distribution falls within two standard deviation (SD) of the mean, then what percentage of the same distribution is less than A + 2SD? A. 68% B. 84% C. 95% D. 97.5% E. 99% OA D Source: e-GMAT ### GMAT/MBA Expert GMAT Instructor Joined 25 Apr 2015 Posted: 2950 messages Followed by: 19 members Upvotes: 43 Top Reply BTGmoderatorDC wrote: The age of a group of people follows a distribution, which is symmetric about the average (mean) A. If 95% of the distribution falls within two standard deviation (SD) of the mean, then what percentage of the same distribution is less than A + 2SD? A. 68% B. 84% C. 95% D. 97.5% E. 99% OA D Source: e-GMAT If 95% of the distribution falls within two standard deviation (SD) of the mean, then 2.5% of the distribution falls more than 2 SDs below the mean (and another 2.5% falls more than 2 SDs above the mean). The percentage of the distribution that is less than A + 2SD is the percentage that falls within 2 SDs of the mean plus the percentage that falls more than 2 SDs below the mean. Therefore, the percentage is 95% + 2.5% = 97.5%. Answer: D _________________ Scott Woodbury-Stewart Founder and CEO scott@targettestprep.com See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews ### GMAT/MBA Expert GMAT Instructor Joined 02 Jun 2008 Posted: 2525 messages Followed by: 352 members Upvotes: 1090 GMAT Score: 780 Top Reply 95% of the distribution is within two standard deviations of the mean, so 95% of the distribution lies between A - 2SD and A + 2SD. So all of those values are less than A+2SD. The other 5% of the distribution is more than two standard deviations from the mean. Since the distribution is symmetric, half of those values, or 2.5% of the entire distribution, will be less than A-2SD, and the rest will be greater than A+2SD. So 95% are between A-2SD and A+2SD, and 2.5% are below A-2SD, for a total of 97.5% that are less than A+2SD. _________________ If you are looking for online GMAT math tutoring, or if you are interested in buying my advanced Quant books and problem sets, please contact me at ianstewartgmat at gmail.com • Award-winning private GMAT tutoring Register now and save up to$200

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