GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 15 Oct 2019, 19:42 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

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.  Each term of set T is a multiple of 5. Is standard deviation

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

Hide Tags

Senior Manager  Joined: 20 Mar 2008
Posts: 396
Each term of set T is a multiple of 5. Is standard deviation  [#permalink]

Show Tags

4
30 00:00

Difficulty:   35% (medium)

Question Stats: 56% (00:51) correct 44% (00:56) wrong based on 469 sessions

HideShow timer Statistics

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

(1) Each term of set T is positive
(2) Set T consists of one term

M08-09
Manager  Joined: 25 Aug 2009
Posts: 138
Re: Each term of set T is a multiple of 5. Is standard deviation  [#permalink]

Show Tags

2
3
my answer is B..

1.) Let T = { 5,15}
Mean = 10
$$sd =\sqrt{\frac{((5 - 10)^2 + (15-10)^2)}{2}}$$

=>$$sd = 5$$ > 0

but, if T = {5,5}
Then Sd = 0 ,, uncertainity,,,hence, insufficient..

2.) T has only one member..
sd = 0 hence, sufficient.. sd is not positive..
General Discussion
Intern  Joined: 27 Aug 2012
Posts: 12
Schools: Anderson '15
Re: Each term of set T is a multiple of 5. Is standard deviation  [#permalink]

Show Tags

Ans is B

1) If pos nos are 5 10 15 the SD>0
If pos nos are same 15 15 15 SD= 0

SD=0 or SD>0

2) Only one number SD= 0
Hence suff to say SD is not greater than zero . SUFFICIENT
VP  Joined: 02 Jul 2012
Posts: 1105
Location: India
Concentration: Strategy
GMAT 1: 740 Q49 V42 GPA: 3.8
WE: Engineering (Energy and Utilities)
Re: Each term of set T is a multiple of 5. Is standard deviation  [#permalink]

Show Tags

1) If T is {5,10,15} then standard deviation is positive. If T is {5,5,5} then standard deviation is 0. Insufficient

2)T contains only one number. Hence standard deviation can only be 0. Sufficient.

_________________
Did you find this post helpful?... Please let me know through the Kudos button.

Thanks To The Almighty - My GMAT Debrief

GMAT Reading Comprehension: 7 Most Common Passage Types
Math Expert V
Joined: 02 Sep 2009
Posts: 58340
Re: Each term of set T is a multiple of 5. Is standard deviation  [#permalink]

Show Tags

1
2
Jivana wrote:
If set $$T$$ consists of odd integers divisible by 5, is the standard deviation of $$T$$ positive?

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

Revised version of this question is below:

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.

_________________
Director  S
Joined: 09 Jun 2010
Posts: 715
Re: Each term of set T is a multiple of 5. Is standard deviation  [#permalink]

Show Tags

I am cheated and fail.

he he,

very easy to die if we are in the test room.

fluency on math must be high
Manager  Joined: 23 Jan 2013
Posts: 128
Concentration: Technology, Other
Schools: Berkeley Haas
GMAT Date: 01-14-2015
WE: Information Technology (Computer Software)
Re: Each term of set T is a multiple of 5. Is standard deviation  [#permalink]

Show Tags

Bunuel wrote:
Jivana wrote:
If set $$T$$ consists of odd integers divisible by 5, is the standard deviation of $$T$$ positive?

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

Revised version of this question is below:

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.

But isn't 0 neither positive nor negative ?? i am confused!!
VP  Status: Far, far away!
Joined: 02 Sep 2012
Posts: 1019
Location: Italy
Concentration: Finance, Entrepreneurship
GPA: 3.8
Re: Each term of set T is a multiple of 5. Is standard deviation  [#permalink]

Show Tags

shelrod007 wrote:
But isn't 0 neither positive nor negative ?? i am confused!!

Indeed my friend.

Bunuel says:

(2) Set T consists of one term --> any set with only one term has the standard deviation equal to zero. As YOU say 0 is neither positive nor negative, so is the standard deviation positive? NO . Sufficient.

The std deviation is 0 and because 0 is not positive or negative, this is sufficient to answer..

Hope this clarifies, let me know
_________________
It is beyond a doubt that all our knowledge that begins with experience.
Kant , Critique of Pure Reason

Tips and tricks: Inequalities , Mixture | Review: MGMAT workshop
Strategy: SmartGMAT v1.0 | Questions: Verbal challenge SC I-II- CR New SC set out !! , My Quant

Rules for Posting in the Verbal Forum - Rules for Posting in the Quant Forum[/size][/color][/b]
Manager  Joined: 07 Apr 2014
Posts: 101
Re: Each term of set T is a multiple of 5. Is standard deviation  [#permalink]

Show Tags

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

(1) Each term of set T is positive
(2) Set T consists of one term

M08-09

1. say terms are 5,5,5,5,5 then SD=0 if 5,10,15 then SD is +ive.. Not suff

2. only one term then SD is zero. hence not +ive--- suff
Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 8007
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: Each term of set T is a multiple of 5. Is standard deviation  [#permalink]

Show Tags

1
Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.

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

(1) Each term of set T is positive
(2) Set T consists of one term

In the original condition, the question asks whether the standard deviation is positive, but standard deviations in general are always greater than or equal to 0. Only when the terms are all equal or when there is only one term will the standard deviation equal 0. Hence, as in condition 2, the set T consists of one term, the standard deviation becomes 0, and the answer to the question becomes 'no' so this is a sufficient condition.
In condition 1, we cannot know whether the terms are equal or different, so this is an insufficient condition, making the answer (B).
This type of question is not normally seen in tests.

Normally, questions regarding standard deviations have too much variables that make (E) the answer, or else the standard deviation becomes 0; only these types of question are normally seen in tests.
_________________
Senior Manager  Joined: 20 Aug 2015
Posts: 387
Location: India
GMAT 1: 760 Q50 V44 Each term of set T is a multiple of 5. Is standard deviation  [#permalink]

Show Tags

1
Jivana wrote:
Each term of set T is a multiple of 5. Is standard deviation of T positive?

(1) Each term of set T is positive
(2) Set T consists of one term

SD in layman terms is the distance between each term and the mean of the set

Given: Each term of the set is a multiple of 5
Required: SD of the set > 0?

Statement 1: Each term of the set is positive
There can be various versions of this set
Set 1: {5, 10, 15}
In this case, SD = 5 (Distance of the elements of the set from the mean)
Set 2: {5, 5, 5}
In this case, SD = 0 (Distance of the elements of the set from the mean)
No unique value of SD

INSUFFICIENT

Statement 2: Set T consists of one term
If there is only one element in the set, then SD = 0
Hence we have a unique value of SD

SUFFICIENT

Director  B
Joined: 04 Jun 2016
Posts: 557
GMAT 1: 750 Q49 V43 Each term of set T is a multiple of 5. Is standard deviation  [#permalink]

Show Tags

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

(1) Each term of set T is positive
(2) Set T consists of one term

M08-09

It's a tricky one.
Standard deviation is never negative. So SD can either be 0 or a positive value.

(1) Each term of set T is positive
{2,2,2,2}==> standard deviation is 0
{1,2,3,4,5} ==> standard deviation will be some positive value.. probably 2.17 or something
INSUFFICIENT

(2) Set T consists of one term
Now thats where it gets tricky .Since standard deviation is the square-root of the unbiased estimator of the variance; it has N-1 in the denominator, where N is the total number of samples; therefore when there is only one sample SD become undefined because N-1 become 1-1=0 and zero is the denominator means undefined values.

SO the answer of this question SHOULD BE E unless we assume that undefined means neither negative, nor positive, nor zero...nor infinity...

Bunuel can you look into the answer ... should w e mark it as B or E
_________________
Posting an answer without an explanation is "GOD COMPLEX". The world doesn't need any more gods. Please explain you answers properly.
FINAL GOODBYE :- 17th SEPTEMBER 2016. .. 16 March 2017 - I am back but for all purposes please consider me semi-retired.
Non-Human User Joined: 09 Sep 2013
Posts: 13168
Re: Each term of set T is a multiple of 5. Is standard deviation  [#permalink]

Show Tags

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________ Re: Each term of set T is a multiple of 5. Is standard deviation   [#permalink] 15 Aug 2019, 01:41
Display posts from previous: Sort by

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

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

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