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

It is currently 23 Jan 2019, 21:13

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 January
PrevNext
SuMoTuWeThFrSa
303112345
6789101112
13141516171819
20212223242526
272829303112
Open Detailed Calendar
  • Key Strategies to Master GMAT SC

     January 26, 2019

     January 26, 2019

     07:00 AM PST

     09:00 AM PST

    Attend this webinar to learn how to leverage Meaning and Logic to solve the most challenging Sentence Correction Questions.
  • Free GMAT Number Properties Webinar

     January 27, 2019

     January 27, 2019

     07:00 AM PST

     09:00 AM PST

    Attend this webinar to learn a structured approach to solve 700+ Number Properties question in less than 2 minutes.

A certain list consists of 21 different numbers. If n is in

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

Hide Tags

 
Manager
Manager
User avatar
Joined: 06 Feb 2010
Posts: 149
Concentration: Marketing, Leadership
Schools: University of Dhaka - Class of 2010
GPA: 3.63
WE: Business Development (Consumer Products)
A certain list consists of 21 different numbers. If n is in  [#permalink]

Show Tags

New post Updated on: 31 Oct 2010, 04:06
24
97
00:00
A
B
C
D
E

Difficulty:

  55% (hard)

Question Stats:

65% (01:09) correct 35% (01:02) wrong based on 1897 sessions

HideShow timer Statistics

A certain list consists of 21 different numbers. If n is in the list and n is 4 times the average(arithmetic mean) of the other 20 numbers in the list, then n is what fraction of the sum of the 21 numbers in the list?

(A) 1/20
(B) 1/6
(C) 1/5
(D) 4/21
(E) 5/21

_________________

Practice Makes a Man Perfect. Practice. Practice. Practice......Perfectly

Critical Reasoning: http://gmatclub.com/forum/best-critical-reasoning-shortcuts-notes-tips-91280.html

Collections of MGMAT CAT: http://gmatclub.com/forum/collections-of-mgmat-cat-math-152750.html

MGMAT SC SUMMARY: http://gmatclub.com/forum/mgmat-sc-summary-of-fourth-edition-152753.html

Sentence Correction: http://gmatclub.com/forum/sentence-correction-strategies-and-notes-91218.html

Arithmatic & Algebra: http://gmatclub.com/forum/arithmatic-algebra-93678.html

Helpful Geometry formula sheet: http://gmatclub.com/forum/best-geometry-93676.html


I hope these will help to understand the basic concepts & strategies. Please Click ON KUDOS Button.


Originally posted by monirjewel on 31 Oct 2010, 03:06.
Last edited by monirjewel on 31 Oct 2010, 04:06, edited 1 time in total.
Most Helpful Expert Reply
Veritas Prep GMAT Instructor
User avatar
D
Joined: 16 Oct 2010
Posts: 8810
Location: Pune, India
Re: A certain list consists  [#permalink]

Show Tags

New post 09 Dec 2010, 04:03
89
30
monirjewel wrote:
A certain list consists of 21 different numbers. If n is in the list and n is 4 times the average(arithmetic mean) of the other 20 numbers in the list, then n is what fraction of the sum of the 21 numbers in the list?

(A) 1/20
(B) 1/6
(C) 1/5
(D) 4/21
(E) 5/21


When you have your answer in percentages/fractions and there are no values in the data given to you, assume values.
Here you do not have the value of any number. So assume 20 numbers are all 1. Their average is 1 and sum is 20.
Then n is 4 and sum of 21 numbers is 24.
4/24 = 1/6
_________________

Karishma
Veritas Prep GMAT Instructor

Learn more about how Veritas Prep can help you achieve a great GMAT score by checking out their GMAT Prep Options >

Most Helpful Community Reply
SVP
SVP
User avatar
Joined: 06 Sep 2013
Posts: 1705
Concentration: Finance
GMAT ToolKit User
Re: A certain list consists of 21 different numbers. If n is in  [#permalink]

Show Tags

New post 30 Dec 2013, 13:17
16
4
monirjewel wrote:
A certain list consists of 21 different numbers. If n is in the list and n is 4 times the average(arithmetic mean) of the other 20 numbers in the list, then n is what fraction of the sum of the 21 numbers in the list?

(A) 1/20
(B) 1/6
(C) 1/5
(D) 4/21
(E) 5/21


n = 4x

where 'x' is the average of other 20 numbers

Then sum of other 20 numbers is 20x

So we get 4x/24x = 1/6

B is our answer

Cheers!
J :)
General Discussion
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 52433
Re: A certain list consists  [#permalink]

Show Tags

New post 31 Oct 2010, 07:08
48
32
monirjewel wrote:
A certain list consists of 21 different numbers. If n is in the list and n is 4 times the average(arithmetic mean) of the other 20 numbers in the list, then n is what fraction of the sum of the 21 numbers in the list?

(A) 1/20
(B) 1/6
(C) 1/5
(D) 4/21
(E) 5/21


Given: \(average_{20}=\frac{sum_{20}}{20}=\frac{n}{4}\) --> \(sum_{20}=5n\) --> \(sum_{21}=sum_{20}+n=5n+n=6n\);

Question: \(n\) is what fraction of the sum of the 21 numbers in the list?
\(\frac{n}{sum_{21}}=\frac{n}{6n}=\frac{1}{6}\).

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

Manager
Manager
avatar
Status: Bunuel's fan!
Joined: 08 Jul 2011
Posts: 157
Re: A certain list consists  [#permalink]

Show Tags

New post 09 Apr 2013, 08:02
1
VeritasPrepKarishma wrote:
monirjewel wrote:
A certain list consists of 21 different numbers. If n is in the list and n is 4 times the average(arithmetic mean) of the other 20 numbers in the list, then n is what fraction of the sum of the 21 numbers in the list?

(A) 1/20
(B) 1/6
(C) 1/5
(D) 4/21
(E) 5/21


When you have your answer in percentages/fractions and there are no values in the data given to you, assume values.
Here you do not have the value of any number. So assume 20 numbers are all 1. Their average is 1 and sum is 20.
Then n is 4 and sum of 21 numbers is 24.
4/24 = 1/6


For this solution, I thought all numbers have to be different?
Veritas Prep GMAT Instructor
User avatar
D
Joined: 16 Oct 2010
Posts: 8810
Location: Pune, India
Re: A certain list consists  [#permalink]

Show Tags

New post 09 Apr 2013, 22:18
7
1
gmatfighter12 wrote:
VeritasPrepKarishma wrote:
monirjewel wrote:
A certain list consists of 21 different numbers. If n is in the list and n is 4 times the average(arithmetic mean) of the other 20 numbers in the list, then n is what fraction of the sum of the 21 numbers in the list?

(A) 1/20
(B) 1/6
(C) 1/5
(D) 4/21
(E) 5/21


When you have your answer in percentages/fractions and there are no values in the data given to you, assume values.
Here you do not have the value of any number. So assume 20 numbers are all 1. Their average is 1 and sum is 20.
Then n is 4 and sum of 21 numbers is 24.
4/24 = 1/6


For this solution, I thought all numbers have to be different?


It usually doesn't matter if the numbers don't need to be integers.
The numbers could be 0.999999999999999, 0.99999998, 1.00000000000000001, 1.000000000002 etc. Effectively, they are all 1 and our solution doesn't change at all.
_________________

Karishma
Veritas Prep GMAT Instructor

Learn more about how Veritas Prep can help you achieve a great GMAT score by checking out their GMAT Prep Options >

Manager
Manager
User avatar
Status: *Lost and found*
Joined: 25 Feb 2013
Posts: 121
Location: India
Concentration: General Management, Technology
GMAT 1: 640 Q42 V37
GPA: 3.5
WE: Web Development (Computer Software)
GMAT ToolKit User
A certain list consists of 21 different numbers. If n is in the  [#permalink]

Show Tags

New post 04 May 2013, 12:22
udaymathapati wrote:
A certain list consists of 21 different numbers. If n is in the list and n is 4 times the average (arithmetic mean) of the other 20 numbers in the list, then n is what fraction of the sum of the 21 numbers in the list?
A. 201
B. 61
C. 51
D. 214
E. 215


Umm 1/6 does seem the answer...udaymathapati could u please confirm the answer and change the choices? well 201 or 61 are not really the proper fractions the question expects.

Regards,
Arpan
_________________

Feed me some KUDOS! :) :) *always hungry*

My Thread : Recommendation Letters

Intern
Intern
avatar
Joined: 27 Jan 2013
Posts: 9
Location: India
Concentration: Strategy, Finance
GMAT 1: 660 Q46 V35
GPA: 3.6
WE: Business Development (Energy and Utilities)
Re: A certain list consists of 21 different numbers. If n is in  [#permalink]

Show Tags

New post 04 Nov 2013, 08:00
This Qs appeared in the newly launched GMAT Exam Prep -1.
GMAC said these Qs were never seen before. What a blatant lie!!!
Senior Manager
Senior Manager
User avatar
Joined: 20 Aug 2015
Posts: 388
Location: India
GMAT 1: 760 Q50 V44
A certain list consists of 21 different numbers. If n is in  [#permalink]

Show Tags

New post 25 Nov 2015, 00:11
6
1
monirjewel wrote:
A certain list consists of 21 different numbers. If n is in the list and n is 4 times the average(arithmetic mean) of the other 20 numbers in the list, then n is what fraction of the sum of the 21 numbers in the list?

(A) 1/20
(B) 1/6
(C) 1/5
(D) 4/21
(E) 5/21


Given: 21 numbers in a list including n. n = 4 times the average of other 20 numbers.
Assume the average to be x
n = 4x - (i)

Average = Sum/20
Sum of other 20 numbers = 20x - (ii)

n/Sum of other 21 numbers = \(\frac{4x}{(4x + 20x)} = \frac{4x}{24x} = 1/6\)
Option B
Intern
Intern
avatar
Joined: 17 Dec 2015
Posts: 1
Re: A certain list consists of 21 different numbers. If n is in  [#permalink]

Show Tags

New post 17 Dec 2015, 14:26
This is how I used to calculate which I think works pretty well:

if you let the average of the 20 other numbers equal a, can you write this equation for sum of the list (S)

n + 20a = S

the question tells us that

n = 4a

plug this back into the first equation and you get that the sum is 24a

4a + 20a = 24a

therefore fraction of n to the total would be

4a/24a or 1/6

answer B
Intern
Intern
avatar
Joined: 12 Dec 2015
Posts: 18
GMAT ToolKit User
A certain list consists of 21 different numbers. If n is in  [#permalink]

Show Tags

New post 04 Mar 2016, 15:54
It is always easier for me to plug-in numbers: Let's say that average of 20 numbers is 10 and each of these 20 numbers is 10. So n term would be 40.

Now the sum of all 21 terms is 20*10+40=240 and the ratio of n to sum of all 21 terms is 40/240=1/6
Manager
Manager
avatar
Joined: 06 Jun 2014
Posts: 89
Location: United States
Concentration: Finance, General Management
GMAT 1: 450 Q27 V21
GPA: 3.47
GMAT ToolKit User
Re: A certain list consists of 21 different numbers. If n is in  [#permalink]

Show Tags

New post 23 Mar 2016, 10:37
I tried to set up an equation and stared at the screen for 1.30 mins. My last try was to use some values and boy it worked :lol:

n= 4(avg of 20#)
let's assume, the avg is 50
n=4(50)
n=200
50(avg of 20#)*20(# in the list) = 1000 + 200(value of n) = 1200

\(\frac{200}{1200}\)

\(\frac{1}{6}\)
Senior Manager
Senior Manager
avatar
Joined: 02 Mar 2012
Posts: 300
Schools: Schulich '16
Re: A certain list consists of 21 different numbers  [#permalink]

Show Tags

New post 02 Jun 2016, 18:20
its B

consider sum of 20 numbers = T

so n= 4*(T/20)=T/5.

Therefore total sum of 21 numbers = T/5+T=6T/5

Now n is what part of total sum of 21 numbers = value of n/value of total 21 numbers=(T/5) / (6T/5) = 1/6
Senior Manager
Senior Manager
User avatar
Joined: 18 Jan 2010
Posts: 251
Re: A certain list consists of 21 different numbers. If n is in  [#permalink]

Show Tags

New post 03 Jun 2016, 00:53
monirjewel wrote:
A certain list consists of 21 different numbers. If n is in the list and n is 4 times the average(arithmetic mean) of the other 20 numbers in the list, then n is what fraction of the sum of the 21 numbers in the list?

(A) 1/20
(B) 1/6
(C) 1/5
(D) 4/21
(E) 5/21



Suppose sum of 20 nos. (excluding n) is S

Then

n = 4 * (\(\frac{S}{20}\))

n = \(\frac{S}{5}\))
5n = S

If we add n to S, we get sum of all 21 nos.

5n+n = Sum of all 21 Nos.

6n = Sum of all 21 nos.

n = (1/6) S.

B is the answer.
EMPOWERgmat Instructor
User avatar
V
Status: GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 13378
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: Q170 V170
Re: A certain list consists of 21 different numbers. If n is in  [#permalink]

Show Tags

New post 03 Jun 2016, 09:28
2
Hi Silviax,

This question can be solved by TESTing VALUES; you'll have to make sure to take the proper notes and label your work to finish it in an efficient way though.

We're told that a list consists of 21 different numbers (N and 20 others) and that N is equal to 4 times the AVERAGE of the other 20 numbers.

Let's TEST:
Average of 20 numbers = 10
Sum of those 20 numbers = 20(10) = 200
N = 4(10) = 40

We're asked to calculate the fraction N/(sum of all 21 numbers) = 40/(200+40) = 40/240 = 1/6

Final Answer:

GMAT assassins aren't born, they're made,
Rich
_________________

760+: Learn What GMAT Assassins Do to Score at the Highest Levels
Contact Rich at: Rich.C@empowergmat.com

Rich Cohen

Co-Founder & GMAT Assassin

Special Offer: Save $75 + GMAT Club Tests Free
  Official GMAT Exam Packs + 70 Pt. Improvement Guarantee
www.empowergmat.com/

*****Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!*****

VP
VP
avatar
P
Joined: 07 Dec 2014
Posts: 1155
A certain list consists of 21 different numbers. If n is in  [#permalink]

Show Tags

New post Updated on: 08 Sep 2018, 11:24
A certain list consists of 21 different numbers. If n is in the list and n is 4 times the average(arithmetic mean) of the other 20 numbers in the list, then n is what fraction of the sum of the 21 numbers in the list?

(A) 1/20
(B) 1/6
(C) 1/5
(D) 4/21
(E) 5/21

let s=sum of 21 numbers
(s-n)/20=n/4
n/s=1/6
B

Originally posted by gracie on 03 Jun 2016, 12:48.
Last edited by gracie on 08 Sep 2018, 11:24, edited 1 time in total.
Manager
Manager
User avatar
Joined: 14 Jun 2012
Posts: 111
Concentration: International Business
GMAT 1: 560 Q36 V31
GMAT 2: 580 Q39 V31
GMAT 3: 630 Q41 V35
GPA: 4
Reviews Badge
A certain list consists of 21 different numbers. If n is in  [#permalink]

Show Tags

New post 05 Jun 2016, 11:09
But I think the problem says that the 21 numbers are all different numbers so they can't all be 10.

I think "test it" is in general a great strategy because it can transform most algebra problems into arithmetic problems which are much easier to solve -at least for me.
EMPOWERgmat Instructor
User avatar
V
Status: GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 13378
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: Q170 V170
Re: A certain list consists of 21 different numbers. If n is in  [#permalink]

Show Tags

New post 06 Jun 2016, 10:23
Hi Silviax,

In my explanation, I did NOT state that the 20 numbers were all 10s - just that the AVERAGE of those numbers was 10. Whatever the individual numbers were, the SUM of those 20 numbers would be (20)(10) = 200.

GMAT assassins aren't born, they're made,
Rich
_________________

760+: Learn What GMAT Assassins Do to Score at the Highest Levels
Contact Rich at: Rich.C@empowergmat.com

Rich Cohen

Co-Founder & GMAT Assassin

Special Offer: Save $75 + GMAT Club Tests Free
  Official GMAT Exam Packs + 70 Pt. Improvement Guarantee
www.empowergmat.com/

*****Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!*****

Manager
Manager
User avatar
Joined: 14 Jun 2012
Posts: 111
Concentration: International Business
GMAT 1: 560 Q36 V31
GMAT 2: 580 Q39 V31
GMAT 3: 630 Q41 V35
GPA: 4
Reviews Badge
Re: A certain list consists of 21 different numbers. If n is in  [#permalink]

Show Tags

New post 06 Jun 2016, 14:47
Yes you are right Rich. I misunderstood what you wrote.
Intern
Intern
avatar
Joined: 05 Apr 2016
Posts: 4
Re: A certain list consists of 21 different numbers. If n is in  [#permalink]

Show Tags

New post 11 Jun 2016, 20:47
EMPOWERgmatRichC wrote:
Hi Silviax,

This question can be solved by TESTing VALUES; you'll have to make sure to take the proper notes and label your work to finish it in an efficient way though.

We're told that a list consists of 21 different numbers (N and 20 others) and that N is equal to 4 times the AVERAGE of the other 20 numbers.

Let's TEST:
Average of 20 numbers = 10
Sum of those 20 numbers = 20(10) = 200
N = 4(10) = 40

We're asked to calculate the fraction N/(sum of all 21 numbers) = 40/(200+40) = 40/240 = 1/6

Final Answer:

GMAT assassins aren't born, they're made,
Rich


Sorry, I am a noob at this and my query could be a stupid one but can you please explain how did you conclude the following:
Average of 20 numbers = 10
Sum of those 20 numbers = 20(10) = 200
GMAT Club Bot
Re: A certain list consists of 21 different numbers. If n is in &nbs [#permalink] 11 Jun 2016, 20:47

Go to page    1   2    Next  [ 32 posts ] 

Display posts from previous: Sort by

A certain list consists of 21 different numbers. If n is in

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


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®.