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

It is currently 22 Feb 2019, 14:45

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 February
PrevNext
SuMoTuWeThFrSa
272829303112
3456789
10111213141516
17181920212223
242526272812
Open Detailed Calendar
  • Free GMAT RC Webinar

     February 23, 2019

     February 23, 2019

     07:00 AM PST

     09:00 AM PST

    Learn reading strategies that can help even non-voracious reader to master GMAT RC. Saturday, February 23rd at 7 AM PT
  • FREE Quant Workshop by e-GMAT!

     February 24, 2019

     February 24, 2019

     07:00 AM PST

     09:00 AM PST

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

What is the greatest prime factor of 1+2+3+….+36?

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

Hide Tags

 
Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6985
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
What is the greatest prime factor of 1+2+3+….+36?  [#permalink]

Show Tags

New post 08 Oct 2018, 00:53
00:00
A
B
C
D
E

Difficulty:

  15% (low)

Question Stats:

77% (00:49) correct 23% (01:06) wrong based on 65 sessions

HideShow timer Statistics

[Math Revolution GMAT math practice question]

What is the greatest prime factor of \(1+2+3+….+36\)?

\(A. 2\)
\(B. 3\)
\(C. 9\)
\(D. 31\)
\(E. 37\)

_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $149 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Director
Director
User avatar
P
Joined: 18 Jul 2018
Posts: 679
Location: India
Concentration: Finance, Marketing
WE: Engineering (Energy and Utilities)
Premium Member Reviews Badge CAT Tests
Re: What is the greatest prime factor of 1+2+3+….+36?  [#permalink]

Show Tags

New post 08 Oct 2018, 01:15
Sum = n(n+1)/2. Sum = 36(37)/2 = 18*37.

Prime factoring gives 3^2*2*37.

Greatest prime factor = 37.

E is the answer

Posted from my mobile device
_________________

Press +1 Kudo If my post helps!

Director
Director
User avatar
G
Joined: 20 Feb 2015
Posts: 795
Concentration: Strategy, General Management
Premium Member
Re: What is the greatest prime factor of 1+2+3+….+36?  [#permalink]

Show Tags

New post 08 Oct 2018, 03:27
MathRevolution wrote:
[Math Revolution GMAT math practice question]

What is the greatest prime factor of \(1+2+3+….+36\)?

\(A. 2\)
\(B. 3\)
\(C. 9\)
\(D. 31\)
\(E. 37\)


sum can be written as
36*37/2 = 37 * 18
greatest prime factor = 37
E
VP
VP
User avatar
P
Joined: 31 Oct 2013
Posts: 1162
Concentration: Accounting, Finance
GPA: 3.68
WE: Analyst (Accounting)
Re: What is the greatest prime factor of 1+2+3+….+36?  [#permalink]

Show Tags

New post 08 Oct 2018, 04:16
MathRevolution wrote:
[Math Revolution GMAT math practice question]

What is the greatest prime factor of \(1+2+3+….+36\)?

\(A. 2\)
\(B. 3\)
\(C. 9\)
\(D. 31\)
\(E. 37\)



The challenge is that how we can determine the sum of this serious. we can do it by applying the following formula.

36 + 1 = 37

35 + 2 = 37

at the same way we can make such pair. we will have 18 pairs as total we have is 36 integers.

37*18 = total. NO need to multiply.

*** 37 is a prime. So it's the greatest prime.

The best answer is E.
GMATH Teacher
User avatar
G
Status: GMATH founder
Joined: 12 Oct 2010
Posts: 772
What is the greatest prime factor of 1+2+3+….+36?  [#permalink]

Show Tags

New post 08 Oct 2018, 04:50
MathRevolution wrote:
[Math Revolution GMAT math practice question]

What is the greatest prime factor of \(1+2+3+….+36\)?

\(A. 2\)
\(B. 3\)
\(C. 9\)
\(D. 31\)
\(E. 37\)

\(?\,\,\,:\,\,\,{\rm{greatest}}\,\,{\rm{prime}}\,\,{\rm{factor}}\)

\(1 + 2 + 3 + \ldots + 36\,\,\mathop = \limits^{\left( * \right)} \,\,\left( {{{1 + 36} \over 2}} \right) \cdot 36 = 18 \cdot 37\,\,\,\,\mathop \Rightarrow \limits^{2,3\,\,{\rm{or}}\,\,37} \,\,\,\,? = 37\)

(*) 1, 2, 3, ..., 36 is a finite arithmetic sequence, hence their average is equal to the average of the first and last terms (or any two symmetric to the median).
Besides that, the sum 1+2+3+...+36 is equal to the average (explained above) times the number of parcels (36), due to the homogeneity nature of the average.


This solution follows the notations and rationale taught in the GMATH method.

Regards,
Fabio.
_________________

Fabio Skilnik :: GMATH method creator (Math for the GMAT)
Our high-level "quant" preparation starts here: https://gmath.net

CEO
CEO
User avatar
D
Joined: 11 Sep 2015
Posts: 3447
Location: Canada
Re: What is the greatest prime factor of 1+2+3+….+36?  [#permalink]

Show Tags

New post 08 Oct 2018, 05:37
Top Contributor
MathRevolution wrote:
[Math Revolution GMAT math practice question]

What is the greatest prime factor of \(1+2+3+….+36\)?

\(A. 2\)
\(B. 3\)
\(C. 9\)
\(D. 31\)
\(E. 37\)


Useful formula: 1 + 2 + 3 + 4 + . . . . + n = (n)(n + 1)/2

So, 1 + 2 + 3 + …. + 36 = (36)(36 + 1)/2
= (36)(37)/2
= (18)(37)
= (2)(3)(3)(17)

So, the greatest prime factor is 37

Answer: E

Cheers,
Brent
_________________

Test confidently with gmatprepnow.com
Image

Manager
Manager
avatar
S
Joined: 24 Dec 2017
Posts: 182
Location: India
Concentration: Strategy, Real Estate
Schools: Johnson '21
Re: What is the greatest prime factor of 1+2+3+….+36?  [#permalink]

Show Tags

New post 08 Oct 2018, 06:07
Formula: 1st term + Last term/2 x number of terms in the series

Let's apply it
=>(1+36)/2 x 36
=>37 x 18 = 666

From the above, we can arrive at the answer.

Greatest prime factor is 37 (E)
Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6985
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
Re: What is the greatest prime factor of 1+2+3+….+36?  [#permalink]

Show Tags

New post 09 Oct 2018, 23:59
=>

Since \(1 + 2 + 3 + … + n = \frac{n(n+1)}{2}\), we have \(1 + 2 + 3 + … + 36 = \frac{(36*37)}{2} = 18*37 = 2*32*37.\)
Thus, \(37\) is the greatest prime factor of \(2*3^2*37.\)

Therefore, the answer is E.
Answer: E
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $149 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

GMAT Club Bot
Re: What is the greatest prime factor of 1+2+3+….+36?   [#permalink] 09 Oct 2018, 23:59
Display posts from previous: Sort by

What is the greatest prime factor of 1+2+3+….+36?

  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®.