BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

GMATPrep DS Problem

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Senior | Next Rank: 100 Posts
Posts: 80
Joined: Wed Jun 04, 2008 1:16 pm
Thanked: 3 times

GMATPrep DS Problem

by mpaudena » Sat Mar 07, 2009 3:15 am
A certain list of data has an average (arithmetic mean) 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 of 102 data with a 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

Thanks in advance for helping. Please let me know why it works. I think I am missing the standard deviation concept. Taking test in 2 hours. Please no abbreviations as I may not understand it and need to get the quick answer right before going in. Thanks.
Top
Source: — Data Sufficiency |
User avatar
Site Admin
Posts: 2567
Joined: Thu Jan 01, 2009 10:05 am
Thanked: 712 times
Followed by:550 members
GMAT Score:770

by DanaJ » Sat Mar 07, 2009 4:12 am
Standard deviation is a concept that refers to the average distance between elements of the series and the arithmetic mean. In order to make it smaller, then you should add numbers to the series that are as close to the mean as possible, since that would minimize the distance between the added elements and the mean.
Now, since the mean is 6, you want to add numbers that are as close as possible to 6. This is why E would be your best bet: the distance between 6 and 6 is, obviously, zero, meaning that the new standard deviation will be reduced (look at the standard deviation formula if you want an algebraic explanation)
Is my answer consistent with the OA?

BTW, good luck with your exam!
Top
Post new topic Post Reply
• Page 1 of 1