Find all School-related info fast with the new School-Specific MBA Forum

It is currently 22 Jul 2014, 14:02

Close

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
Your Progress

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

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

What is the SD of the set: a, b, c, d 1) a+b+c+d=50 2)

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Manager
Manager
avatar
Joined: 07 May 2007
Posts: 181
Followers: 1

Kudos [?]: 6 [0], given: 0

GMAT Tests User
What is the SD of the set: a, b, c, d 1) a+b+c+d=50 2) [#permalink] New post 17 Jun 2007, 08:36
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions
What is the SD of the set: a, b, c, d

1) a+b+c+d=50
2) a^2+b^2+c^2+d^2=200
Director
Director
User avatar
Joined: 26 Feb 2006
Posts: 908
Followers: 3

Kudos [?]: 36 [0], given: 0

GMAT Tests User
Re: DS - Standard Deviation [#permalink] New post 17 Jun 2007, 12:32
iamba wrote:
What is the SD of the set: a, b, c, d

1) a+b+c+d=50
2) a^2+b^2+c^2+d^2=200


Which one is correct?
a^2+b^2+c^2+d^2 = 200 or
a^2+b^2+c^2+d^2 = 2000?
Manager
Manager
avatar
Joined: 28 Aug 2006
Posts: 160
Followers: 1

Kudos [?]: 10 [0], given: 0

GMAT Tests User
 [#permalink] New post 19 Jun 2007, 19:53
SD can be measured if you have sum of the numbers and sum of the sqaures of the numbers using the following formula

SD= SQRT ((SumX^2/N) -(SumX/N)^2)
Applying this SQRT(2000/4-(50/2)^2)

I think Sum of sqaures should be 2000
Director
Director
User avatar
Joined: 26 Feb 2006
Posts: 908
Followers: 3

Kudos [?]: 36 [0], given: 0

GMAT Tests User
 [#permalink] New post 19 Jun 2007, 19:58
iamba wrote:
a^2 + b^2 + c^2 + d^2 = 200


if (a + b + c + d) = 50, how (a^2 + b^2 + c^2 + d^2) = 200? cuz a or b or c or d could be +ve or -ve, but a^2, b^2, c^2, and d^2 can not be -ve. they all are positive.

the minimum value = 4 (12.5)^2 = 625 when a = b = c = d. if a, b, c and d are different from 12.5, the value of (a^2 + b^2 + c^2 + d^2) will be grater than 625.

can you explain where i am i missing?
Manager
Manager
avatar
Joined: 07 May 2007
Posts: 181
Followers: 1

Kudos [?]: 6 [0], given: 0

GMAT Tests User
 [#permalink] New post 19 Jun 2007, 20:18
I guess it should be 2000, even though my question booklet has 200. But does this info really required to answer the Q?
Manager
Manager
avatar
Joined: 23 May 2007
Posts: 109
Followers: 1

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

GMAT Tests User
 [#permalink] New post 19 Jun 2007, 21:11
Is this formula required ???
SD= SQRT ((SumX^2/N) -(SumX/N)^2)

or theres anoher way
Manager
Manager
avatar
Joined: 07 May 2007
Posts: 181
Followers: 1

Kudos [?]: 6 [0], given: 0

GMAT Tests User
 [#permalink] New post 19 Jun 2007, 22:18
This is how I approached it

Mean = 50/4 = 12.5

SD = SQRT{(12.5-a)^2+...........)/4}

which takes the form of

SD = SQRT{ (4*12.5^2-12.5(a+b+c+d)+a^2+b^2+c^2+d^2)/4}

Plug in the values to get SD
Director
Director
User avatar
Joined: 26 Feb 2006
Posts: 908
Followers: 3

Kudos [?]: 36 [0], given: 0

GMAT Tests User
 [#permalink] New post 20 Jun 2007, 09:08
vijay2001 wrote:
SD can be measured if you have sum of the numbers and sum of the sqaures of the numbers using the following formula

SD= SQRT ((SumX^2/N) -(SumX/N)^2)
Applying this SQRT(2000/4-(50/2)^2)

I think Sum of sqaures should be 2000


SD = SQRT ((SumX^2 / N) - (SumX / N)^2)
SD = SQRT[(2,000/4) - (50 / 4)^2]
SD = sqrt (343.75)
SD = 18.54

so C.
  [#permalink] 20 Jun 2007, 09:08
    Similar topics Author Replies Last post
Similar
Topics:
1 DS Q There is set of consecutive even integers. What is S.D? abhi47 2 31 Jan 2012, 01:28
c^d=(1/c)^(3d-8) what is the value of c^d? a) c=4 b) d= ArvGMAT 2 05 Aug 2006, 19:21
2^20 - n is divisible by 3, what can n be? A. 0 B. 1 C. 2 D. laxieqv 7 13 Apr 2006, 09:02
If a=2b, 1/2b=c, and 4c=3d, then what is the ratio of d to GMATT73 3 16 Oct 2005, 04:12
What is the standard deviation of the set: a, b, c, d 1) pb_india 5 14 Jan 2005, 08:21
Display posts from previous: Sort by

What is the SD of the set: a, b, c, d 1) a+b+c+d=50 2)

  Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Privacy Policy| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

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®.