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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 ## Standard deviation ##### This topic has 1 expert reply and 4 member replies A certain list of 100 data has an average of 6 and a standard deviation of d, where d is positive. Which of the following pairs of data, when added to the list, must result in a list 0f 102 data with standard deviation less than d? A. -6 and 0 B. 0 and 0 C. 0 and 6 D. 0 and 12 E. 6 and 6 OA E Can anyone explain this in detail? Legendary Member Joined 13 Mar 2010 Posted: 576 messages Followed by: 1 members Upvotes: 97 Standard deviation shows the is difference between the mean and the values,more the values closer to mean,lesser will be standard deviation. here the adding two values will make the sd lower mean ,since mean is 6 deviation of values will be lesser if the list have more number of values equal to mean(variance 0) ans option E _________________ “If you don't know where you are going, any road will get you there.” Lewis Carroll Senior | Next Rank: 100 Posts Joined 15 Aug 2009 Posted: 85 messages Upvotes: 19 my approach: sd= rt ((avg-x)^2...)/n) to decrease the sd, we need to decrease the numerator and increase the denominator which is increased to 102 to decrease the numerator, we need to decrease the the number squared, so the closer the number is to the avg, the lower the square that occurs with choice e Newbie | Next Rank: 10 Posts Joined 16 May 2010 Posted: 7 messages Upvotes: 1 Test Date: 6/12/2010 Target GMAT Score: 760 GMAT Score: 740 liferocks wrote: Standard deviation shows the is difference between the mean and the values,more the values closer to mean,lesser will be standard deviation. here the adding two values will make the sd lower mean ,since mean is 6 deviation of values will be lesser if the list have more number of values equal to mean(variance 0) ans option E Agree with this answer. This is a question that tests subject knowledge instead of computational skill. You must know that standard deviation is the average distance between any given point in the set and the mean of the set. If you want a smaller standard deviation, you need numbers that are closer to the mean, on average, than the rest of the set. _________________ MGMAT1: 720 (Q47, V41) GMATPrep1: 750 (Q48, V44) GMATPrep2: 770 (Q50, V47) Master | Next Rank: 500 Posts Joined 29 Mar 2010 Posted: 214 messages Upvotes: 37 GMAT Score: 700 Think about it like this; the only way you can increase the data set and decrease the standard deviation (the amount the data deviates from average) would be to add two numbers that equal the average, or are very close to the average. Thus, E is correct. ### GMAT/MBA Expert GMAT Instructor Joined 21 May 2010 Posted: 1053 messages Followed by: 98 members Upvotes: 335 I agree with the solutions advanced. NO math is Standard deviation roughly measures the average distance between the mean and every value. To minimize standard deviation, the values added must be as close to the mean as possible. In this case the mean is 6, so the new values that would minimize standard deviation are 6 and 6. The answer is E. Look for topic="Statistics" and difficulty="500-600" to find similar questions in the drill generator. This is GMATPrep question 1155 Good luck, -Patrick _________________ Ask me about tutoring. • FREE GMAT Exam Know how you'd score today for$0

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