NEW HERE? LEARN MORE
closeclose
Last visit was: 23 Apr 2024, 15:23 It is currently 23 Apr 2024, 15:23
Decision Tracker
My Rewards
New posts
New comers' posts

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.
Go to My Error Log Learn more
Close
Request Expert Reply
Confirm Cancel

M11-09

SORT BY:
Date
Kudos
Tags:
Find Similar Topics 
Show Tags
Hide Tags
User avatar
L
Bunuel
Math Expert
Joined: 02 Sep 2009
Posts: 92883
Own Kudos [?]: 618585 [23]
Given Kudos: 81563
Send PM
CAT Tests Forum Quiz Mode
M11-09 [#permalink] New post   16 Sep 2014, 00:44
2
Kudos
21
Bookmarks
Expert Reply
00:00
A
B
C
D
E

Difficulty:

45% (medium)

Question Stats:

64% (01:24) correct 36% (01:08) wrong based on 174 sessions
Hide Show 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. \(\{ab + c, \ a(1 + b), \ b(1+a)\}\)
ShowHide Answer
Official Answer
E
Most Helpful Reply
User avatar
L
Bunuel
Math Expert
Joined: 02 Sep 2009
Posts: 92883
Own Kudos [?]: 618585 [7]
Given Kudos: 81563
Send PM
CAT Tests Forum Quiz Mode
Re: M11-09 [#permalink] New post   12 Jun 2020, 00:11
1
Kudos
6
Bookmarks
Expert Reply
davidbeckham wrote:
Bunuel - I have a very basic doubt on solving quant questions generally. How do we know when to pick numbers and when to solve the question directly, just by looking at the question? I tried picking up numbers for this question and wasted a lot of time in the process and didn't even get the answer in the first place.


Check the links below:

Backsolving on GMAT Math
How to Plug in Numbers on GMAT Math Questions
Why Approximate?
GMAT Math Strategies — Estimation, Rounding and other Shortcuts
The Power of Estimation for GMAT Quant
The 4 Math Strategies Everyone Must Master, Part 1 (1. Test Cases and 2. Choose Smart Numbers.)
The 4 Math Strategies Everyone Must Master, part 2 (3. Work Backwards and 4. Estimate)
Intelligent Guessing on GMAT
How to Avoid Tedious Calculations on the Quantitative Section of the GMAT
GMAT Tip of the Week: No Calculator? No Problem.
The Importance of Sorting Answer Choices on the GMAT
Identifying the Correct Answer on GMAT Quant Questions
How to Manage Unmanageable Numbers on the GMAT
Should You Double Check Your Answer Choices on the GMAT?
User avatar
L
Bunuel
Math Expert
Joined: 02 Sep 2009
Posts: 92883
Own Kudos [?]: 618585 [5]
Given Kudos: 81563
Send PM
CAT Tests Forum Quiz Mode
Re M11-09 [#permalink] New post   16 Sep 2014, 00:44
2
Kudos
3
Bookmarks
Expert Reply
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.

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


Answer: E
General Discussion
avatar
rhio
Intern
Intern
Joined: 25 Apr 2015
Posts: 6
Own Kudos [?]: 2 [0]
Given Kudos: 36
Schools: ISB '17 NTU '17 NUS '18 SMU '17 Cass '17 WBS '18
Send PM
Re: M11-09 [#permalink] New post   09 Dec 2015, 15:25
What about choice A? {ab, b2, cb} = b{a,b,c)?
User avatar
Shrivathsan
Manager
Manager
Joined: 15 Apr 2016
Posts: 51
Own Kudos [?]: 101 [0]
Given Kudos: 66
Send PM
Re: M11-09 [#permalink] 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 ---
User avatar
Senthil7
Senior Manager
Senior Manager
Joined: 31 Mar 2016
Posts: 325
Own Kudos [?]: 195 [0]
Given Kudos: 197
Location: India
Concentration: Operations, Finance
GMAT 1: 670 Q48 V34
GPA: 3.8
WE:Operations (Commercial Banking)
Send PM
GMAT ToolKit User
Re: M11-09 [#permalink] New post   06 Aug 2016, 11:13
I think this is a high-quality question and I agree with explanation.
User avatar
B
RenanBragion
Current Student
Joined: 01 Jun 2020
Posts: 127
Own Kudos [?]: 8 [0]
Given Kudos: 12
Location: Brazil
Schools: Wharton '23 (D) Sloan '23 (M) Kellogg '23 (A) CBS '23 (D)
GMAT 1: 760 Q48 V46
Send PM
Reviews Badge
Re: M11-09 [#permalink] New post   07 Jun 2020, 09:21
I think this is a high-quality question and I agree with explanation.
User avatar
S
davidbeckham
Stanford School Moderator
Joined: 11 Jun 2019
Posts: 113
Own Kudos [?]: 56 [0]
Given Kudos: 181
Location: India
Send PM
Reviews Badge
Re: M11-09 [#permalink] New post   11 Jun 2020, 22:29
Bunuel - I have a very basic doubt on solving quant questions generally. How do we know when to pick numbers and when to solve the question directly, just by looking at the question? I tried picking up numbers for this question and wasted a lot of time in the process and didn't even get the answer in the first place.
User avatar
S
kaladin123
Current Student
Joined: 06 Jul 2019
Posts: 135
Own Kudos [?]: 59 [0]
Given Kudos: 747
Location: India
Concentration: General Management, Strategy
Schools: IIMA PGPX'23 (II)
GMAT 1: 640 Q39 V39
GMAT 2: 700 Q48 V38 (Online)
GPA: 3.11
WE:Project Management (Computer Software)
Send PM
Reviews Badge
Re: M11-09 [#permalink] New post   03 Jun 2021, 19:04
I think this is a high-quality question and I agree with the explanation.
avatar
B
RRJ12
Intern
Intern
Joined: 06 Sep 2020
Posts: 20
Own Kudos [?]: 3 [0]
Given Kudos: 278
Location: India
GMAT 1: 640 Q48 V31
Send PM
Re: M11-09 [#permalink] New post   06 Jun 2021, 07:16
Why is C wrong ? Adding/ subtracting "A" from each should not change the answer?
User avatar
L
Bunuel
Math Expert
Joined: 02 Sep 2009
Posts: 92883
Own Kudos [?]: 618585 [0]
Given Kudos: 81563
Send PM
CAT Tests Forum Quiz Mode
Re: M11-09 [#permalink] New post   06 Jun 2021, 09:44
Expert Reply
RRJ12 wrote:
Why is C wrong ? Adding/ subtracting "A" from each should not change the answer?


The SD will not change if we ONLY add or ONLY subtract a constant from each term in a set. In C we are subtracting from a from a and c but adding a to b.
User avatar
L
Bunuel
Math Expert
Joined: 02 Sep 2009
Posts: 92883
Own Kudos [?]: 618585 [0]
Given Kudos: 81563
Send PM
CAT Tests Forum Quiz Mode
Re: M11-09 [#permalink] New post   18 Jun 2023, 14:23
Expert Reply
I have edited the question and the solution by adding more details to enhance its clarity. I hope it is now easier to understand.
GMAT Club Bot
gmatclubot
Re: M11-09 [#permalink]
18 Jun 2023, 14:23
Moderator:
Bunuel
Math Expert
92883 posts

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne
Main navigation
GMAT Resources
Partners
MBA Resources
www.gmac.com|www.mba.com | | GMAT Club Rules | Terms and Conditions