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

It is currently 16 Jan 2019, 02:44

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
  • The winning strategy for a high GRE score

     January 17, 2019

     January 17, 2019

     08:00 AM PST

     09:00 AM PST

    Learn the winning strategy for a high GRE score — what do people who reach a high score do differently? We're going to share insights, tips and strategies from data we've collected from over 50,000 students who used examPAL.
  • Free GMAT Strategy Webinar

     January 19, 2019

     January 19, 2019

     07:00 AM PST

     09:00 AM PST

    Aiming to score 760+? Attend this FREE session to learn how to Define your GMAT Strategy, Create your Study Plan and Master the Core Skills to excel on the GMAT.

If N = 1/3 + 1/3^2 +1/3^3 , then N is between

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

Hide Tags

 
Retired Moderator
avatar
Joined: 29 Oct 2013
Posts: 260
Concentration: Finance
GPA: 3.7
WE: Corporate Finance (Retail Banking)
GMAT ToolKit User
If N = 1/3 + 1/3^2 +1/3^3 , then N is between  [#permalink]

Show Tags

New post 28 Dec 2015, 23:06
1
5
00:00
A
B
C
D
E

Difficulty:

  15% (low)

Question Stats:

77% (00:55) correct 23% (00:52) wrong based on 218 sessions

HideShow timer Statistics

If N = 1/3 + 1/3^2 +1/3^3 , then N is between

A. 0 and 1/9
B. 1/9 and 1/3
C. 1/3 and 8/9
D. 8/9 and 4/3
E. 4/3 and 2

_________________

Please contact me for super inexpensive quality private tutoring

My journey V46 and 750 -> http://gmatclub.com/forum/my-journey-to-46-on-verbal-750overall-171722.html#p1367876

Math Expert
User avatar
V
Joined: 02 Aug 2009
Posts: 7199
Re: If N = 1/3 + 1/3^2 +1/3^3 , then N is between  [#permalink]

Show Tags

New post 28 Dec 2015, 23:16
NoHalfMeasures wrote:
If N = 1/3 + 1/3^2 +1/3^3 , then N is between

A. 0 and 1/9
B. 1/9 and 1/3
C. 1/3 and 8/9
D. 8/9 and 4/3
E. 4/3 and 2



hi,
the Q is simple and can be done with simple addition..

N = 1/3 + 1/3^2 +1/3^3 =1/3 + 1/9 +1/27= (9+3+1)/27=13/27, which is clearly close to 1/2
and will fit in range of 1/3 and 8/9..
if a number is series or contains a large number of fractions we can work on estimate to get the answer..

N = 1/3 + 1/3^2 +1/3^3 ..
two values which can be easily seen are Min and Max ..
N>1/3 and N<1.. only C and D fit in..
Each term in N is 1/3 of the pervious term so cannot be closer to 1..
only C is left
_________________

1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html


GMAT online Tutor

Retired Moderator
avatar
Joined: 29 Oct 2013
Posts: 260
Concentration: Finance
GPA: 3.7
WE: Corporate Finance (Retail Banking)
GMAT ToolKit User
If N = 1/3 + 1/3^2 +1/3^3 , then N is between  [#permalink]

Show Tags

New post 28 Dec 2015, 23:18
1
chetan2u

I know its an easy question.

but I decided to go a little pedantic in case gmat asks a more challenging question of this type :)

It is a geometric progression with a=r= 1/3

sum=1/3* {1- (1/3)^n}/{1-(1/3)} = 13/27 ~ less than .50

Ans C
_________________

Please contact me for super inexpensive quality private tutoring

My journey V46 and 750 -> http://gmatclub.com/forum/my-journey-to-46-on-verbal-750overall-171722.html#p1367876

EMPOWERgmat Instructor
User avatar
V
Status: GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 13326
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: Q170 V170
Re: If N = 1/3 + 1/3^2 +1/3^3 , then N is between  [#permalink]

Show Tags

New post 30 Dec 2015, 10:24
1
Hi All,

In certain Quant questions, the answer choices are designed to provide a significant 'shortcut' (so that you can avoid some of the 'math' involved if you recognize the pattern/concept that the question is built around).

Here, we're asked to think about the sum of 1/3 + 1/3^2 +1/3^3, but we're not actually asked to calculate it. The prompt asks for the RANGE that this total would fall into.

Since we're adding up 1/3 + 1/9 + 1/27, we can see that each fraction becomes significantly SMALLER than the one before it. If we were adding 1/3 + 1/3 + 1/3, then we'd have a total of 1. Here, the second two fractions are MUCH SMALLER than 1/3, so the total has to be FAR LESS than 1 (but greater than 1/3). There's only one answer that matches this deduction.

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!*****

Manager
Manager
User avatar
B
Joined: 23 Jul 2014
Posts: 88
Location: India
WE: Information Technology (Computer Software)
Re: If N = 1/3 + 1/3^2 +1/3^3 , then N is between  [#permalink]

Show Tags

New post 03 Jan 2016, 06:05
1
I did by inference
if we add [1/9 = .11] to [1/3=.33] .. it gives .44
now we add [1/27~ 1/25 = .04] to .44 it gives .48 ~.5
now it does not drift 1/3 much from its position and it should stay close to 1/3
hence only one possible answer C
_________________

The Mind ~ Muscle Connection
My GMAT Journey is Complete.Going to start the MBA in Information Management from 2016
Good Luck everyone.

EMPOWERgmat Instructor
User avatar
V
Status: GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 13326
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: Q170 V170
Re: If N = 1/3 + 1/3^2 +1/3^3 , then N is between  [#permalink]

Show Tags

New post 03 Jan 2016, 11:28
Hi tryambaks,

The ability to convert Quant data/information from one 'format' to another will be quite helpful on a handful of questions on Test Day, so you should continue to look for opportunities to use those skills as you practice.

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!*****

Intern
Intern
avatar
B
Joined: 14 Oct 2016
Posts: 32
Location: India
WE: Sales (Energy and Utilities)
Premium Member
Re: If N = 1/3 + 1/3^2 +1/3^3 , then N is between  [#permalink]

Show Tags

New post 09 Sep 2017, 22:08
1
there are two methods of doing this each method can take upto 50 Secs

First Method
1/3= 33.33%
1/9= 11.11%
1/27 will be 1/9( 33.33%) 3.70 %

addding we get it will be nearly equal to 49 % so the answer will be what

Each choice can be read as

A 0 and 1/9 can be read as 0% to 11% ( No)
B.1/9 and 1/3 can be read as 11% to 33% ( No)
C.1/3 and 8/9 can be read as 33% to 88% ( Ok seems in our range)
D.8/9 and 4/3 can be read as 88% to 133% ( No)
E. 4/3 and 2 can be read as 133% to 200% ( No)


Second method
if we can see the series is as GP then sum is given by
a{1-(r)^n}/{1-r}

a= 1/3 , r=1/3

Now 1/3{1-1/27}/{1-1/3}
={26/27*3}2/3
= 13/27

ok so 13/26 = 1/2=.5 and 13/26>13/27 so thus value is slightly less than .5
So only option C it says between .333 to .8888
_________________

Abhimanyu

Target Test Prep Representative
User avatar
G
Status: Head GMAT Instructor
Affiliations: Target Test Prep
Joined: 04 Mar 2011
Posts: 2830
Re: If N = 1/3 + 1/3^2 +1/3^3 , then N is between  [#permalink]

Show Tags

New post 14 Dec 2017, 18:05
NoHalfMeasures wrote:
If N = 1/3 + 1/3^2 +1/3^3 , then N is between

A. 0 and 1/9
B. 1/9 and 1/3
C. 1/3 and 8/9
D. 8/9 and 4/3
E. 4/3 and 2



We can add together the given equation:

n = 1/3 + 1/3^2 + 1/3^3

n = 1/3 + 1/9 + 1/27

n = 9/27 + 3/27 + 1/27 = 13/27

We see that 13/27 is just under 1/2, thus n is between 1/3 and 8/9.

Answer: C
_________________

Jeffery Miller
Head of GMAT Instruction

GMAT Quant Self-Study Course
500+ lessons 3000+ practice problems 800+ HD solutions

Manager
Manager
avatar
S
Joined: 11 Feb 2018
Posts: 201
GMAT 1: 690 Q47 V37
GMAT 2: 710 Q50 V36
GMAT 3: 750 Q50 V42
Re: If N = 1/3 + 1/3^2 +1/3^3 , then N is between  [#permalink]

Show Tags

New post 04 Jan 2019, 19:56
No need to even do any addition i think for this question...

1/3 is >> 1/9
1/3 is >>>1/27

So essentially we are adding 2 very small quantities to 1/3.This addition therefore wont exceed 1/3 by a large amount.Therefore C

Posted from my mobile device
Intern
Intern
avatar
B
Joined: 26 Nov 2018
Posts: 10
Re: If N = 1/3 + 1/3^2 +1/3^3 , then N is between  [#permalink]

Show Tags

New post 04 Jan 2019, 20:05
Sum of infinite GP is
a/1-a
(1/3)/{1-(1/3)}=1/2
Clearly C is answer

Posted from my mobile device
GMAT Club Bot
Re: If N = 1/3 + 1/3^2 +1/3^3 , then N is between &nbs [#permalink] 04 Jan 2019, 20:05
Display posts from previous: Sort by

If N = 1/3 + 1/3^2 +1/3^3 , then N is between

  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®.