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

It is currently 17 Jun 2018, 18:54

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

Events & Promotions in June
Open Detailed Calendar

M11-09

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

Hide Tags

Expert Post
2 KUDOS received
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 46035
M11-09 [#permalink]

Show Tags

New post 16 Sep 2014, 00:44
2
7
00:00
A
B
C
D
E

Difficulty:

  55% (hard)

Question Stats:

57% (00:41) correct 43% (00:57) wrong based on 124 sessions

HideShow timer Statistics

Which of the following sets must have the same standard deviation as set \(\{a, \ b, \ c\}\)?

A. \(\{ab, \ b^2, \ cb\}\)
B. \(\{2a, \ b + a, \ c + b\}\)
C. \(\{0, \ b + a, \ c - a\}\)
D. \(\{ab, \ bc, \ ac\}\)
E. \(\{ab + c, \ a(1 + b), \ b(1+a)\}\)

_________________

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

Expert Post
2 KUDOS received
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 46035
Re M11-09 [#permalink]

Show Tags

New post 16 Sep 2014, 00:44
2
1
Official Solution:

Which of the following sets must have the same standard deviation as set \(\{a, \ b, \ c\}\)?

A. \(\{ab, \ b^2, \ cb\}\)
B. \(\{2a, \ b + a, \ c + b\}\)
C. \(\{0, \ b + a, \ c - a\}\)
D. \(\{ab, \ bc, \ ac\}\)
E. \(\{ab + c, \ a(1 + b), \ b(1+a)\}\)


If we add or subtract a constant to each term in a set the standard deviation will not change.

Notice that set \(\{ab + c, \ a(1 + b), \ b(1+a)\}=\{c+ab, \ a+ab, \ b+ab\}\), so this set is obtained by adding some number \(ab\) to each term of set \(\{a, \ b, \ c\}\), which means that those sets must have the same standard deviation.


Answer: E
_________________

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: 25 Apr 2015
Posts: 10
Re: M11-09 [#permalink]

Show Tags

New post 09 Dec 2015, 15:25
What about choice A? {ab, b2, cb} = b{a,b,c)?
Senior Manager
Senior Manager
avatar
S
Joined: 18 Aug 2014
Posts: 324
GMAT ToolKit User Reviews Badge
Re: M11-09 [#permalink]

Show Tags

New post 03 May 2016, 13:25
rhio wrote:
What about choice A? {ab, b2, cb} = b{a,b,c)?


This is what I did
_________________

Please help me find my lost Kudo's bird

Manager
Manager
User avatar
Joined: 15 Apr 2016
Posts: 83
Re: M11-09 [#permalink]

Show Tags

New post 20 Jun 2016, 09:59
rhio wrote:
What about choice A? {ab, b2, cb} = b{a,b,c)?



Hi Rhio,

Multiplication changes the standard deviation.
Here we are multiplying everything with b which means even the SD is being multiplies with b.

Hope this helps :)

-------------------------
Shrivathsan
GMAT 700 it is ---
_________________

Cheers,
Shri
-------------------------------
GMAT is not an Exam... it is a war .. Let's Conquer !!!

Senior Manager
Senior Manager
User avatar
Joined: 31 Mar 2016
Posts: 401
Location: India
Concentration: Operations, Finance
GMAT 1: 670 Q48 V34
GPA: 3.8
WE: Operations (Commercial Banking)
GMAT ToolKit User Premium Member
Re M11-09 [#permalink]

Show Tags

New post 06 Aug 2016, 11:13
I think this is a high-quality question and I agree with explanation.
Intern
Intern
avatar
Joined: 27 Oct 2015
Posts: 19
Re: M11-09 [#permalink]

Show Tags

New post 16 Dec 2016, 20:35
Please can someone explain why Choice D {ab,bc, ac} is incorrect?

Many Thanks
Expert Post
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 46035
Re: M11-09 [#permalink]

Show Tags

New post 17 Dec 2016, 03:53
Intern
Intern
avatar
B
Joined: 07 Feb 2016
Posts: 21
GMAT 1: 650 Q47 V34
GMAT 2: 710 Q48 V39
Re: M11-09 [#permalink]

Show Tags

New post 01 May 2017, 22:25
Bunuel wrote:
dsheth7 wrote:
Please can someone explain why Choice D {ab,bc, ac} is incorrect?

Many Thanks


Why should {ab, bc, ac} have the same SD as {a, b, c}? You can substitute numbers to check that's it won't always be true.


As already mentioned, the standard deviation does not change when a specific value is added/subtracted from ALL values of the set. Multiplication/division is changing the standard deviation.
Intern
Intern
avatar
B
Joined: 25 Oct 2017
Posts: 1
CAT Tests
Re: M11-09 [#permalink]

Show Tags

New post 21 May 2018, 08:46
Why is choice B incorrect?
{2a,a+b,c+a} means a is being added to each number of the set
Expert Post
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 46035
Re: M11-09 [#permalink]

Show Tags

New post 21 May 2018, 08:53
Intern
Intern
avatar
B
Joined: 06 May 2018
Posts: 33
Re: M11-09 [#permalink]

Show Tags

New post 21 May 2018, 09:11
Test numbers. That helps. For example 5,10, 15. For answer choice c you get 65,55,60. As you can easily see, the deviation is the same.
Manager
Manager
avatar
B
Joined: 29 Sep 2017
Posts: 77
Location: United States
Concentration: Strategy, Leadership
GPA: 3.3
WE: Consulting (Consulting)
GMAT ToolKit User Reviews Badge
Re: M11-09 [#permalink]

Show Tags

New post 08 Jun 2018, 15:08
2 quick ways to solve:

1. Pick small numbers
2. Follow bunnel's solution (recognize the pattern in E)

I went with 1 and took 2:43 to solve this which is very much above what it should take. The question is... how does one spot patterns quickly (rhetorical)?
_________________

If this helped, please give kudos!

Re: M11-09   [#permalink] 08 Jun 2018, 15:08
Display posts from previous: Sort by

M11-09

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

Moderators: chetan2u, Bunuel



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®.