It is currently 19 Mar 2018, 09:48

### 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

# Set T consists of a certain number of even integers

 post reply Question banks Downloads My Bookmarks Reviews Important topics
Author Message
Manager
Joined: 09 Oct 2008
Posts: 93
Set T consists of a certain number of even integers [#permalink]

### Show Tags

19 Oct 2008, 05:44
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

Set T consists of a certain number of even integers divisible by 3. Is standard deviation of T positive?

1:All elements of set T are positive
2:The range of set T is 0
SVP
Joined: 29 Aug 2007
Posts: 2457
Re: Standard Deviation [#permalink]

### Show Tags

19 Oct 2008, 07:29
vishalgc wrote:
Set T consists of a certain number of even integers divisible by 3. Is standard deviation of T positive?

1:All elements of set T are positive
2:The range of set T is 0

B.

1: T could have diffierent or same +ve integers. nsf...
2: T has same +ve integers. so range = 0. Hence T has zero (0) or non-positive SD. suff.
_________________

Gmat: http://gmatclub.com/forum/everything-you-need-to-prepare-for-the-gmat-revised-77983.html

GT

VP
Joined: 17 Jun 2008
Posts: 1328
Re: Standard Deviation [#permalink]

### Show Tags

19 Oct 2008, 07:49
vishalgc wrote:
Set T consists of a certain number of even integers divisible by 3. Is standard deviation of T positive?

1:All elements of set T are positive
2:The range of set T is 0

2)solves the issue since 0 = range means all equal values !!!SD=0 which is neither +ve nor -ve
1)All elements are +ve means the deviation is always +ve irrespective of individual values!!!

IMO D

one doubt is that I thought SD is always +ve since its RMS value of deviations !!!Please clearify and is the AREA of the graph !!
_________________

cheers
Its Now Or Never

Manager
Joined: 16 Jan 2008
Posts: 99
Re: Standard Deviation [#permalink]

### Show Tags

19 Oct 2008, 11:14
IMO A

still same doubt! Where did you get this que from?
Senior Manager
Joined: 21 Apr 2008
Posts: 479
Schools: Kellogg, MIT, Michigan, Berkeley, Marshall, Mellon
Re: Standard Deviation [#permalink]

### Show Tags

19 Oct 2008, 11:26
Me too.

I would bet all my money to say that SD is always +ive

SD=sqrt(sum((xi-mean)^2))

How can be it -ive?

What is the source of the problem?

Cheers
_________________

mates, please visit my profile and leave comments
http://gmatclub.com/forum/johnlewis1980-s-profile-feedback-is-more-than-welcome-80538.html

I'm not linked to GMAT questions anymore, so, if you need something, please PM me

I'm already focused on my application package

My experience in my second attempt
http://gmatclub.com/forum/p544312#p544312
My experience in my third attempt
http://gmatclub.com/forum/630-q-47-v-28-engineer-non-native-speaker-my-experience-78215.html#p588275

Manager
Joined: 14 Jan 2006
Posts: 87
Schools: HKUST
Re: Standard Deviation [#permalink]

### Show Tags

19 Oct 2008, 16:36
1
KUDOS
IMO B

1.) T= (6,12). i.e SD>0
or
T = (6,6,6). i.e, SD = 0
Insuff

2.) all the numbers are same
Therefore, SD = 0
Suff..
Senior Manager
Joined: 18 Jun 2007
Posts: 281
Re: Standard Deviation [#permalink]

### Show Tags

20 Oct 2008, 02:30
This is a wrong question. SD is always positive.
The basic idea of the standard deviation is that you're measuring variations around the mean value. Some of those values will be below the mean, some above and sometimes you'll have some that are equal to the mean. In other words some of the differences between the individual measurements will be positive (more than the mean), some will be negative (below the mean) and some will be zero (directly equal to the mean). Now just adding these differences up is dangerous because the positive and negative values will cancel each other out. For example, to take an incredibly simplistic case, if you've got a sample of two values, one of 9 and one of 11, the mean is equal to 10. The differences are -1 and +1, adding these together gives us a total variation of 0. But we know that there's not zero variation around that mean value!

So, to get round this problem each of the variations around the mean is squared. When you square a negative value you get a positive value.

I am great... and you can sue my Leo sun for that statement
VP
Joined: 30 Jun 2008
Posts: 1019
Re: Standard Deviation [#permalink]

### Show Tags

20 Oct 2008, 02:52
Calculation of Standard Deviation (SD):
i) Find the mean of the set of numbers
ii) Find the difference between each of the numbers and the mean
iii) Square the differences and take the mean of the differences
iv) Take the positive square root of this value

_________________

"You have to find it. No one else can find it for you." - Bjorn Borg

SVP
Joined: 29 Aug 2007
Posts: 2457
Re: Standard Deviation [#permalink]

### Show Tags

20 Oct 2008, 05:08
rishi2377 wrote:
This is a wrong question. SD is always positive.

SD can be 0, which is not +ve.
_________________

Gmat: http://gmatclub.com/forum/everything-you-need-to-prepare-for-the-gmat-revised-77983.html

GT

Senior Manager
Joined: 21 Apr 2008
Posts: 479
Schools: Kellogg, MIT, Michigan, Berkeley, Marshall, Mellon
Re: Standard Deviation [#permalink]

### Show Tags

20 Oct 2008, 09:49
GMAT TIGER wrote:
rishi2377 wrote:
This is a wrong question. SD is always positive.

SD can be 0, which is not +ve.

mmm, good point GMAT TIGER. I didn't see it

if I consider the problem again, taking into account that SD can be 0 or greater than 0:

1 Suff. because all elements are greater than 0. The solution is "yes"

2 Suff. because the range equals 0 means that the maximum number and the minimum are equal. Therefore, SD = 0. Answer "no"

However, I get 2 different answers which I think is not possible on a real GMAT exam, isn't it?
_________________

mates, please visit my profile and leave comments
http://gmatclub.com/forum/johnlewis1980-s-profile-feedback-is-more-than-welcome-80538.html

I'm not linked to GMAT questions anymore, so, if you need something, please PM me

I'm already focused on my application package

My experience in my second attempt
http://gmatclub.com/forum/p544312#p544312
My experience in my third attempt
http://gmatclub.com/forum/630-q-47-v-28-engineer-non-native-speaker-my-experience-78215.html#p588275

Re: Standard Deviation   [#permalink] 20 Oct 2008, 09:49
Display posts from previous: Sort by

# Set T consists of a certain number of even integers

 post reply Question banks Downloads My Bookmarks Reviews Important topics

Moderator: chetan2u

 Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne 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®.