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Register now and save up to $200 Available with Beat the GMAT members only code • 5 Day FREE Trial Study Smarter, Not Harder Available with Beat the GMAT members only code • Free Veritas GMAT Class Experience Lesson 1 Live Free Available with Beat the GMAT members only code ## List M(not shown) consists of 8 different integers, each of This topic has 2 expert replies and 0 member replies eitijan Master | Next Rank: 500 Posts Joined 30 Jan 2016 Posted: 157 messages Upvotes: 1 #### List M(not shown) consists of 8 different integers, each of Thu Mar 03, 2016 6:09 am 4, 6, 8f 10,12, 14, 16,18, 20, 22 List M(not shown) consists of 8 different integers,each of which is in the list shown. What is the standard deviation of the numbers in list M? (1) The average (arithmetic mean) of the numbers in list M is equal to the average of the numbers in the list shown. (2) List Mdoes not contain 22. For the list of 10 nos, mean = Mean of 8 terms (M) = 13 Statement 1: Here, S(n terms)= n/2{2a+(n-1)d} where, n= no of terms in the list a= first term of the list d= constant difference of the term with the succeeding term Mean= Sum/n 13= (8/2[2a + 7*2])/8 This gives value of a=6 Also, S(n terms) = n/2[a+l] where, l = last term of the list 13= 8/2[6+l]/8 gives l =20 i.e. we know the list M and so Statement 1 is sufficient. Please correct me if I am wrong as OA is not A but C. ### GMAT/MBA Expert GMATGuruNY GMAT Instructor Joined 25 May 2010 Posted: 14026 messages Followed by: 1812 members Upvotes: 13060 GMAT Score: 790 Thu Mar 03, 2016 8:27 am Quote: 4, 6, 8, 10, 12, 14, 16, 18, 20, 22 List M(not shown) consists of 8 different integers, each of which is in the list shown(above). What is the standard deviation of the numbers in list M? (1) The average (arithmetic mean) of the numbers in list M is equal to the average of the numbers in the list shown. (2) List M does not contain 22. Thanks The list above contains 10 integers. List M contains 8 of these integers. To determine the standard deviation of list M, we need to know WHICH 2 INTEGERS from the list above are NOT included in list M. For any set of evenly spaced numbers: average = median = (biggest+smallest)/2. sum = number*average. Thus, for the list of 10 integers above: Average = (4+22)/2 = 13. Sum = 10*13 = 130. Statement 1: The average (arithmetic mean) of the numbers in list M is equal to the average of the numbers in the list shown. Thus, the average of the 8 integers in list M = 13. Sum = 8*13 = 104. Since the sum of the 8 integers in list M (104) is 26 less than the sum of the 10 integers in the list above (130), the 2 integers NOT included in list M must have a sum of 26. Thus, any of the following could be the pair NOT included in list M: 4+22, 6+20, 8+18, 10+16, 12+14. INSUFFICIENT. Statement 2: List M does not contain 22. No way to determine the OTHER integer not included in list M. INSUFFICIENT. Statements 1 and 2 combined: Since the 2 integers not included in list M must have a sum of 26, and 22 is one of these integers, the other integer not included in list M must be 4. SUFFICIENT. The correct answer is C. _________________ Mitch Hunt GMAT Private Tutor GMATGuruNY@gmail.com If you find one of my posts helpful, please take a moment to click on the "UPVOTE" icon. Available for tutoring in NYC and long-distance. For more information, please email me at GMATGuruNY@gmail.com. Free GMAT Practice Test How can you improve your test score if you don't know your baseline score? Take a free online practice exam. Get started on achieving your dream score today! Sign up now. ### GMAT/MBA Expert DavidG@VeritasPrep Legendary Member Joined 14 Jan 2015 Posted: 2667 messages Followed by: 120 members Upvotes: 1153 GMAT Score: 770 Thu Mar 03, 2016 6:33 am eitijan wrote: 4, 6, 8, 10,12, 14, 16,18, 20, 22 List M(not shown) consists of 8 different integers,each of which is in the list shown. What is the standard deviation of the numbers in list M? (1) The average (arithmetic mean) of the numbers in list M is equal to the average of the numbers in the list shown. (2) List Mdoes not contain 22. For the list of 10 nos, mean = Mean of 8 terms (M) = 13 Statement 1: Here, S(n terms)= n/2{2a+(n-1)d} where, n= no of terms in the list a= first term of the list d= constant difference of the term with the succeeding term Mean= Sum/n 13= (8/2[2a + 7*2])/8 This gives value of a=6 Also, S(n terms) = n/2[a+l] where, l = last term of the list 13= 8/2[6+l]/8 gives l =20 i.e. we know the list M and so Statement 1 is sufficient. Please correct me if I am wrong as OA is not A but C. The problem with this approach is that the formula is for evenly spaced sets, but we don't know if M is evenly spaced. All we know is that the mean is 13. So you could have the set: 6, 8, 10,12, 14, 16,18, 20. (If it's evenly spaced.) But you could also have: 4, 8, 10,12, 14, 16,18, 22. These sets will have different standard deviations. So the statement alone is not sufficient. _________________ Veritas Prep | GMAT Instructor Veritas Prep Reviews Save$100 off any live Veritas Prep GMAT Course

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