SD : GMAT Data Sufficiency (DS)
Check GMAT Club App Tracker for the Latest School Decision Releases http://gmatclub.com/AppTrack

 It is currently 10 Dec 2016, 22:38

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# SD

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics
Author Message
TAGS:

### Hide Tags

Intern
Joined: 18 May 2011
Posts: 17
Followers: 0

Kudos [?]: 1 [1] , given: 13

### Show Tags

29 May 2011, 10:16
1
KUDOS
00:00

Difficulty:

(N/A)

Question Stats:

86% (01:36) correct 14% (00:40) wrong based on 7 sessions

### HideShow timer Statistics

Hi All,
I chose C for this one but the correct answer is A. Can someone please help explain why?

Thanks!
[Reveal] Spoiler: OA

Attachments

question.JPG [ 66.85 KiB | Viewed 1408 times ]

Math Forum Moderator
Joined: 20 Dec 2010
Posts: 2021
Followers: 162

Kudos [?]: 1672 [0], given: 376

### Show Tags

29 May 2011, 11:38
Carol680 wrote:
Hi All,
I chose C for this one but the correct answer is A. Can someone please help explain why?

Thanks!

Please search before posting. Almost all gmatprep questions are already discussed.

Refer:
gmat-prep-ds-q-94166.html
math-standard-deviation-87905.html
_________________
Intern
Joined: 18 May 2011
Posts: 17
Followers: 0

Kudos [?]: 1 [0], given: 13

### Show Tags

01 Jun 2011, 01:57
thangduong wrote:
it is best to remember the formular of the SD= square of (1/n (a1-x)^2 + (a2-x)^2+.........)

from 1, now we replace a1 with 0.7 a1, x with 0.7 x as condition 1 tell us. Every thing reduce to 0.7

it is clear we can find new SD. DONT COUNT, just know it is sufficient.

from 2, we can not know the square of diffence between each number and average in the new set. not sufficient.

thank you very much
Re: SD   [#permalink] 01 Jun 2011, 01:57
Similar topics Replies Last post
Similar
Topics:
What is the standard deviation (SD) of the four numbers 1 18 Jun 2013, 21:08
4 What is SD of given set of numbers whose average is 5? 5 31 Oct 2010, 04:26
Display posts from previous: Sort by

# SD

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics

 Powered by phpBB © phpBB Group and phpBB SEO Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.