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

It is currently 15 Dec 2018, 08:45

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.

Close

Request Expert Reply

Confirm Cancel
Events & Promotions in December
PrevNext
SuMoTuWeThFrSa
2526272829301
2345678
9101112131415
16171819202122
23242526272829
303112345
Open Detailed Calendar
  • $450 Tuition Credit & Official CAT Packs FREE

     December 15, 2018

     December 15, 2018

     10:00 PM PST

     11:00 PM PST

    Get the complete Official GMAT Exam Pack collection worth $100 with the 3 Month Pack ($299)
  • FREE Quant Workshop by e-GMAT!

     December 16, 2018

     December 16, 2018

     07:00 AM PST

     09:00 AM PST

    Get personalized insights on how to achieve your Target Quant Score.

D01-18

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

Hide Tags

Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 51218
D01-18  [#permalink]

Show Tags

New post 15 Sep 2014, 23:12
00:00
A
B
C
D
E

Difficulty:

  65% (hard)

Question Stats:

53% (00:40) correct 47% (00:46) wrong based on 197 sessions

HideShow timer Statistics

Set \(S\) consists of \(N\) elements. If \(N \gt 2\), what is the standard deviation of \(S\)?


(1) The mean and median of the set are positive

(2) The difference between any two elements of the set is equal

_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 51218
Re D01-18  [#permalink]

Show Tags

New post 15 Sep 2014, 23:12
Official Solution:


Statement 1: If the mean and median of the set are positive, the standard deviation could be any. The set could have elements {1, 1, 1} or {1, 2, 3} or {10, 20, 30, 40, 50}. In each case, the standard deviation is not the same. So not sufficient..

Statement 2: If difference between any elements of the set is equal, then the set has to have same elements because the number of elements is greater than 2. So standard deviation is 0. Sufficient.


Answer: B
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

Intern
Intern
avatar
B
Joined: 20 Jun 2013
Posts: 8
Concentration: Finance
GMAT Date: 12-20-2014
GPA: 3.71
Re: D01-18  [#permalink]

Show Tags

New post 02 Dec 2014, 11:20
Bunuel wrote:
Official Solution:


Statement 1: If the mean and median of the set is positive, the standard deviation could be any. The set could have elements {1, 1, 1} or {1, 2, 3} or {10, 20, 30, 40, 50}. In each case, the standard deviation isn’t the same. So NSF.

Statement 2: If difference between any elements of the set is equal, then the set has to have same elements because the number of elements is greater than 2. So standard deviation is 0. Sufficient.


Answer: B


Statement 2: If difference between any elements of the set is equal, then the set has to have same elements because the number of elements is greater than 2. So standard deviation is 0. Sufficient.


I'm confused why they have to be the same elements because the number of elements is greater than 2.. If the difference is equal, can't it just be {1,3,5..} or {1,5,9..} which means SD can be anything..

Also, can you explain difference between elements and numbers in this case? This may be adding to my confusion.
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 51218
Re: D01-18  [#permalink]

Show Tags

New post 03 Dec 2014, 03:06
3
codeblue wrote:
Bunuel wrote:
Official Solution:


Statement 1: If the mean and median of the set is positive, the standard deviation could be any. The set could have elements {1, 1, 1} or {1, 2, 3} or {10, 20, 30, 40, 50}. In each case, the standard deviation isn’t the same. So NSF.

Statement 2: If difference between any elements of the set is equal, then the set has to have same elements because the number of elements is greater than 2. So standard deviation is 0. Sufficient.


Answer: B


Statement 2: If difference between any elements of the set is equal, then the set has to have same elements because the number of elements is greater than 2. So standard deviation is 0. Sufficient.


I'm confused why they have to be the same elements because the number of elements is greater than 2.. If the difference is equal, can't it just be {1,3,5..} or {1,5,9..} which means SD can be anything..

Also, can you explain difference between elements and numbers in this case? This may be adding to my confusion.


Second statement says that the difference between ANY two elements of the set is equal. If the set does not have all the elements equal, for example, if the set is {1, 3, 5}, then the difference between ANY two elements of the set won't be equal: 3-1=2 but 5-1=4. Hence the set must have same elements.

As for your other question: element of a set and number of a set are the same thing - member of a set.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

Intern
Intern
avatar
B
Joined: 16 Apr 2013
Posts: 8
GMAT 1: 760 Q49 V45
Reviews Badge
Re: D01-18  [#permalink]

Show Tags

New post 18 Jan 2015, 13:11
Given statement 1, can we conclude Set S is evenly spaced?
Current Student
avatar
Joined: 04 Mar 2015
Posts: 6
Location: Pakistan
Concentration: Marketing, Operations
GMAT 1: 670 Q45 V37
GPA: 3.5
WE: Engineering (Energy and Utilities)
Re: D01-18  [#permalink]

Show Tags

New post 27 Mar 2015, 10:05
Statement mentions that mean and median are equal not positive as mentioned in the answer explanation.
Current Student
avatar
Joined: 04 Mar 2015
Posts: 6
Location: Pakistan
Concentration: Marketing, Operations
GMAT 1: 670 Q45 V37
GPA: 3.5
WE: Engineering (Energy and Utilities)
Re: D01-18  [#permalink]

Show Tags

New post 27 Mar 2015, 10:05
1
Statement mentions that mean and median are equal not positive as mentioned in the answer explanation.
Intern
Intern
avatar
Joined: 06 Nov 2014
Posts: 31
Re: D01-18  [#permalink]

Show Tags

New post 05 Jul 2015, 17:04
Bunuel wrote:
Official Solution:


Statement 1: If the mean and median of the set is positive, the standard deviation could be any. The set could have elements {1, 1, 1} or {1, 2, 3} or {10, 20, 30, 40, 50}. In each case, the standard deviation is not the same. So NSF.

Statement 2: If difference between any elements of the set is equal, then the set has to have same elements because the number of elements is greater than 2. So standard deviation is 0. Sufficient.


Answer: B


Suppose n=2
Then what will happen for Statement ii)

Consider a case {1,2}

2-1=1 and 1-2 =-1 .
The difference is not the same correct ??
So in a way I am disproving the given statement and this approach is incorrect.

If Set {1,1}

difference is always 0. Therefore SD is 0.

Are there other possibilities or other insights to this ? I want to understand the n=2 case better.
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 51218
Re: D01-18  [#permalink]

Show Tags

New post 06 Jul 2015, 00:05
anurag356 wrote:
Bunuel wrote:
Official Solution:


Statement 1: If the mean and median of the set is positive, the standard deviation could be any. The set could have elements {1, 1, 1} or {1, 2, 3} or {10, 20, 30, 40, 50}. In each case, the standard deviation is not the same. So NSF.

Statement 2: If difference between any elements of the set is equal, then the set has to have same elements because the number of elements is greater than 2. So standard deviation is 0. Sufficient.


Answer: B


Suppose n=2
Then what will happen for Statement ii)

Consider a case {1,2}

2-1=1 and 1-2 =-1 .
The difference is not the same correct ??
So in a way I am disproving the given statement and this approach is incorrect.

If Set {1,1}

difference is always 0. Therefore SD is 0.

Are there other possibilities or other insights to this ? I want to understand the n=2 case better.


Question says that n > 2, why are you considering n = 2 there?
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

Intern
Intern
avatar
Joined: 06 Nov 2014
Posts: 31
Re: D01-18  [#permalink]

Show Tags

New post 06 Jul 2015, 01:29
1
Bunuel wrote:
anurag356 wrote:
Bunuel wrote:
Official Solution:


Statement 1: If the mean and median of the set is positive, the standard deviation could be any. The set could have elements {1, 1, 1} or {1, 2, 3} or {10, 20, 30, 40, 50}. In each case, the standard deviation is not the same. So NSF.

Statement 2: If difference between any elements of the set is equal, then the set has to have same elements because the number of elements is greater than 2. So standard deviation is 0. Sufficient.


Answer: B


Suppose n=2
Then what will happen for Statement ii)

Consider a case {1,2}

2-1=1 and 1-2 =-1 .
The difference is not the same correct ??
So in a way I am disproving the given statement and this approach is incorrect.

If Set {1,1}

difference is always 0. Therefore SD is 0.

Are there other possibilities or other insights to this ? I want to understand the n=2 case better.


Question says that n > 2, why are you considering n = 2 there?



Its true that N>2 is given.

But if in the exam no such condition was given then I ll have to consider 2 elements in a set as well.In that case what will happen is what Im trying to understand. So that I can be prepared.

To understand things better im asking this case.
Intern
Intern
avatar
Joined: 28 Aug 2014
Posts: 3
Location: Brazil
Concentration: General Management, Leadership
GMAT ToolKit User
Re: D01-18  [#permalink]

Show Tags

New post 12 Aug 2015, 18:51
1
Official Solution:


Statement 1: If the mean and median of the set is positive, the standard deviation could be any. The set could have elements {1, 1, 1} or {1, 2, 3} or {10, 20, 30, 40, 50}. In each case, the standard deviation is not the same. So NSF.

Statement 2: If difference between any elements of the set is equal, then the set has to have same elements because the number of elements is greater than 2. So standard deviation is 0. Sufficient.


Answer: B
Statement mentions that mean and median are equal not positive as mentioned in the answer explanation.
Intern
Intern
avatar
Joined: 11 Oct 2016
Posts: 3
D01-18  [#permalink]

Show Tags

New post 04 Jul 2017, 22:09
Even if the constraint x>2 was not given, option ii would still be sufficient right?
I am not sure how x>2 helps the second option.
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 51218
Re: D01-18  [#permalink]

Show Tags

New post 04 Jul 2017, 22:34
pg1 wrote:
Even if the constraint x>2 was not given, option ii would still be sufficient right?
I am not sure how x>2 helps the second option.


If the number of elements is 0 or 1, the second statement won't make any sense. If the number of elements were 2, the question would be much easier.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

Manager
Manager
avatar
G
Joined: 28 Jun 2018
Posts: 147
Location: India
Concentration: Finance, Marketing
Schools: CUHK '21 (II)
GMAT 1: 650 Q49 V30
GPA: 4
GMAT ToolKit User Premium Member Reviews Badge CAT Tests
Re: D01-18  [#permalink]

Show Tags

New post 07 Aug 2018, 05:58
Bunuel , I have one doubt, It might be stupid but still I have it
When we say 'Set' --> doesn't it mean a collection of distinct objects. So how come , we are taking Set as {1,1,1} as per second statement.
Doesn't it violate basic definition of Set?
_________________

What to do if you are new to GMAT:
https://gmatclub.com/forum/what-to-do-if-you-are-new-272708.html#p2108758

GMAC official guides : https://gmatclub.com/forum/gmac-official-guides-the-master-directory-links-240610.html#p1854935

Give me kudos if you like it , it's totally harmless :)

GMAT Club Bot
Re: D01-18 &nbs [#permalink] 07 Aug 2018, 05:58
Display posts from previous: Sort by

D01-18

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

Moderators: chetan2u, Bunuel



Copyright

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

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®.