Check GMAT Club Decision Tracker for the Latest School Decision Releases https://gmatclub.com/AppTrack

 It is currently 27 May 2017, 03:49

### 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

# DS: STDs (m08q09)

Author Message
Manager
Joined: 27 Apr 2010
Posts: 121
Followers: 0

Kudos [?]: 94 [0], given: 61

### Show Tags

10 Apr 2012, 21:03
I'm not going to go into "how to solve" since many others are do it much better than I do.

I think for this question the key factors to know are:
1) definition of standard definition
2) definition of "0"

remember, when all numbers are the same or if there is one number in the set, the standard deviation is 0.
0 is not a positive integer. (positive integer is > 0).
Manager
Joined: 10 Jan 2011
Posts: 240
Location: India
GMAT Date: 07-16-2012
GPA: 3.4
WE: Consulting (Consulting)
Followers: 0

Kudos [?]: 63 [0], given: 25

### Show Tags

11 Apr 2012, 00:23
HG wrote:
Standard deviation is always postivie . It's a average distance from mean. Distance can't be negative

1 - Suff
2- St dev is 0 - Suff

D

Yes St daviation can be positive or zero. Please note that zero is neighter positive nor negative.

A is not suff as STD can be positive or negative
B is suff as STD is 0

IMO ANS B
_________________

-------Analyze why option A in SC wrong-------

Manager
Status: I will not stop until i realise my goal which is my dream too
Joined: 25 Feb 2010
Posts: 229
Schools: Johnson '15
Followers: 2

Kudos [?]: 53 [0], given: 16

### Show Tags

12 Apr 2012, 07:12
snkrhed wrote:
I'm not going to go into "how to solve" since many others are do it much better than I do.

I think for this question the key factors to know are:
1) definition of standard definition
2) definition of "0"

remember, when all numbers are the same or if there is one number in the set, the standard deviation is 0.
0 is not a positive integer. (positive integer is > 0).

SD problems are the ones i miss and i failed here too....
_________________

Regards,
Harsha

Note: Give me kudos if my approach is right , else help me understand where i am missing.. I want to bell the GMAT Cat

Satyameva Jayate - Truth alone triumphs

Math Expert
Joined: 02 Sep 2009
Posts: 38910
Followers: 7741

Kudos [?]: 106291 [0], given: 11620

### Show Tags

11 Apr 2013, 05:09
Set $$T$$ consists of odd integers divisible by 5. Is standard deviation of $$T$$ positive?

1. All members of $$T$$ are positive
2. $$T$$ consists of only one member

[Reveal] Spoiler: OA
B

Source: GMAT Club Tests - hardest GMAT questions

On a side note, when a question tells you a set S has numbers x,y,z - do we assume that x y z will always be different numbers? or can they be the same number, but repeated 3 times.

BELOW IS REVISED VERSION OF THIS QUESTION:

Each term of set T is a multiple of 5. Is standard deviation of T positive?

The standard deviation of a set shows how much variation there is from the mean, how widespread a given set is. So, a low standard deviation indicates that the data points tend to be very close to the mean, whereas high standard deviation indicates that the data are spread out over a large range of values. So, basically we can say that it in a sense measures the distance and the distance can not be negative, which means that the standard deviation of any set is greater than or equal to zero: .

Next, the standard deviation of a set is zero if and only the set consists of identical numbers (or which is the same if the set consists of only one number).

(1) Each term of set T is positive --> if T={5} then then SD=0 but if set T={5, 10} then SD>0. Not sufficient.

(2) Set T consists of one term --> any set with only one term has the standard deviation equal to zero. Sufficient.

_________________
Intern
Joined: 11 Jan 2010
Posts: 38
Followers: 1

Kudos [?]: 53 [0], given: 9

### Show Tags

11 Apr 2013, 05:21
Question: Is SD > 0?
S1: T = {5} => SD = 0 => No
T = (5, 15, 35} => SD > 0 => Yes
S1 is not sufficient.

S2: T = {5) => SD = 0 => No
T = (15) => SD = 0 => No
T = (25) => SD = 0 => No
S2 is sufficient.

B is correct.
Manager
Joined: 31 May 2011
Posts: 203
Followers: 1

Kudos [?]: 2 [0], given: 4

### Show Tags

11 Apr 2013, 05:47
snkrhed wrote:
I'm not going to go into "how to solve" since many others are do it much better than I do.

I think for this question the key factors to know are:
1) definition of standard definition
2) definition of "0"

remember, when all numbers are the same or if there is one number in the set, the standard deviation is 0.
0 is not a positive integer. (positive integer is > 0).

Sorry but is there some mistake here.
Thought this helpful set of Bunuel

math-number-theory-88376.html

Then positive number is a real number greater than 0
And 0 is not negative or positive number. Then in (2) SD = 0 => Why 0 is a positive number.

I find out this revise of Bunuel
ds-stds-m08q09-73347-20.html#p1210600
He also says the answer is B.
Could anyone here explain for me?
Manager
Joined: 31 May 2011
Posts: 203
Followers: 1

Kudos [?]: 2 [0], given: 4

### Show Tags

11 Apr 2013, 05:54
Bunuel wrote:
thaihoang305 wrote:
snkrhed wrote:
I'm not going to go into "how to solve" since many others are do it much better than I do.

I think for this question the key factors to know are:
1) definition of standard definition
2) definition of "0"

remember, when all numbers are the same or if there is one number in the set, the standard deviation is 0.
0 is not a positive integer. (positive integer is > 0).

Sorry but is there some mistake here.
Thought this helpful set of Bunuel

math-number-theory-88376.html

Then positive number is a real number greater than 0
And 0 is not negative or positive number. Then in (2) SD = 0 => Why 0 is a positive number.

I find out this revise of Bunuel
ds-stds-m08q09-73347-20.html#p1210600
He also says the answer is B.
Could anyone here explain for me?

From (2) we get that SD=0, thus the answer to the question "is SD positive" is NO, which makes the second statement sufficient.

Thank you so much Bunuel
Manager
Joined: 15 Aug 2012
Posts: 110
Location: India
Concentration: Technology, Strategy
Schools: Merage '15 (A)
GPA: 3.6
WE: Consulting (Computer Software)
Followers: 6

Kudos [?]: 47 [0], given: 22

### Show Tags

11 Apr 2013, 07:29
Set T consists of odd integers divisible by 5. Is standard deviation of positive?

1. All members of T are positive
2. consists of only one member

for 1. the SD can be 0(all same) or positive(all different). Hence Not Sufficient
for 2. the SD is 0 so sufficient.

Hence IMO B
Intern
Joined: 11 Jan 2010
Posts: 38
Followers: 1

Kudos [?]: 53 [0], given: 9

### Show Tags

11 Apr 2013, 08:18
Although it's true that this problem is tests on the concept or definition of the standard deviation, I think that I'd like to further break up my the evaluation of the two statements. Using the concept, here is how I'd solve this:

Set T = {5 * I} where I = 1, 3, 5, 7, ..., or n
Question: Is SD = positive?
S1: All member of T are positive.
Here are some of rules:
If the set consists of only one item, then SD = 0 (because mean is same as the item).
If the set consists of evenly distributed number, then SD > 0
So, making use of these two rule, we know that this answer is not sufficient.

S2: T consists of only one number.
In this case, we know that SD is always 0. So, the answer to the question is always no.
Therefore, S2 is sufficient.

Re: DS: STDs (m08q09)   [#permalink] 11 Apr 2013, 08:18

Go to page   Previous    1   2   [ 29 posts ]

Similar topics Replies Last post
Similar
Topics:
DS question 0 14 Dec 2011, 05:07
DS q 1 07 Jun 2011, 10:51
DS problem 1 20 Jan 2010, 04:44
DS:m 15 #29 1 23 Jun 2009, 20:23
6 M04 DS # 11 6 10 Jul 2014, 06:28
Display posts from previous: Sort by

# DS: STDs (m08q09)

Moderator: Bunuel

 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®.