Live GMAT classes with Target Test Prep start Nov 21 and Nov 22. First class free.

See classes
Target Test Prep · GMAT

Choose how you want to prepare

Learn live with an expert or move at your own pace. Every option includes the complete TTP study system.

Newsweek Readers’ Choice Awards 2026 winner: Target Test Prep, #1 Test Prep

Target Test Prep was voted #1 Best Test Prep in the 2026 Newsweek Readers’ Choice™ Awards.

★★★★★5.0563 reviews
GMATLiveTeachStarts Nov 22
Josh Braslow, Target Test Prep GMAT expert
LIVE ONLINE CLASSES

Get Ready for GMAT Test Day Faster with Live Online Classes

with Josh Braslow, 20+ years in test prep

Nov 22 · Josh Braslow
Sun · 9:30 AM to 12:30 PM ET
Included
40 hours of live online classes + 6 months of TTP OnDemand
  • Attend the first class for free
  • Every class is recorded, so you never fall behind
View classes & enroll
Limited seats availableTarget Test Prep
EALiveTeachOnDemandStart anytime
EXECUTIVE ASSESSMENT

Target Test Prep EA OnDemand

Self-paced EA prep. Study on your schedule.

EXECUTIVE ASSESSMENT

with

165+ EA score guarantee
$05-day trial no automatic billing
Schedule
Included
40 hours of live online classes plus six months of access to the complete TTP EA OnDemand course.
  • 165+ EA Score Guarantee
  • 4,100+ Quant, Verbal, and Integrated Reasoning practice questions
  • 400+ hours of in-depth video lessons
  • 3,000+ step-by-step video solutions
View EA class & enroll Start free 5-day trial
Limited cohort · enrollment openTrial includes full course accessTarget Test Prep
GMATOnDemandStart anytime
SELF-PACED MASTERCLASS

Target Test Prep GMAT OnDemand

Complete access from day one. Study on your schedule.

715+ score guarantee
$0to start then $127/mo
  • Personalized study plan and analytics
  • Thousands of lessons and practice questions
Start free 5-day trial
Read 563 reviewsTarget Test Prep

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

Expert replies
Post new topic Post Reply
Subscribe topic
Previous Topic Next Topic
User avatar
Elite Legendary Member
Posts: 3991
Joined: Fri Jul 24, 2015 2:28 amFollowed by: 37 members
Location: Las Vegas, USA
Thanked: 19 times
by Max@Math Revolution » Mon Oct 08, 2018 12:49 am
Timer
00:00
Your answer
Difficulty–

right wrong

Pick an answer to see how members did

[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
Top
Join the discussion
Source: — Problem Solving |
User avatar
GMAT Instructor
Posts: 1449
Joined: Sat Oct 09, 2010 2:16 pmFollowed by: 33 members
Thanked: 59 times

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

by fskilnik@GMATH » Mon Oct 08, 2018 4:38 am
Max@Math Revolution 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
$$?\,\,\,:\,\,\,{\rm{greatest}}\,\,{\rm{prime}}\,\,{\rm{factor}}$$
$$1 + 2 + 3 + \ldots + 36\,\,\mathop = \limits^{\left( * \right)} \,\,\left( {{{1 + 36} \over 2}} \right) \cdot 36 = 18 \cdot 37\,\,\,\,\mathop \Rightarrow \limits^{2,3\,\,{\rm{or}}\,\,37} \,\,\,\,? = 37$$
(*) The parcels 1, 2, 3, ..., 36 constitute 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)
English-speakers :: https://www.gmath.net
Portuguese-speakers :: https://www.gmath.com.br
Top
Join the discussion

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 16206
Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members
Location: Vancouver, BC
Thanked: 5254 times
GMAT Score:770

by Brent@GMATPrepNow » Mon Oct 08, 2018 5:34 am
Max@Math Revolution wrote: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
Brent Hanneson - Creator of GMATPrepNow.com
Image
Top
Join the discussion
User avatar
Elite Legendary Member
Posts: 3991
Joined: Fri Jul 24, 2015 2:28 amFollowed by: 37 members
Location: Las Vegas, USA
Thanked: 19 times

by Max@Math Revolution » Tue Oct 09, 2018 11:49 pm
=>

Since 1 + 2 + 3 + … + n = n(n+1)/2, we have 1 + 2 + 3 + … + 36 = (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
Top
Join the discussion

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 8246
Joined: Sat Apr 25, 2015 10:56 amFollowed by: 29 members
Location: Los Angeles, CA
Thanked: 43 times

by Scott@TargetTestPrep » Wed Oct 10, 2018 5:48 pm
Max@Math Revolution 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
We can find the sum of this equally-spaced set by first determining the average of the set and then multiplying the average by the number of items in the set. We calculate the average as: (smallest number + greatest number)/2. We note that there are 36 numbers in the set. Thus, we have:

(1+2+3+….+36) = (1 + 36)/2 x 36 = 37 x 18 = 37 x 2 x 3^2

So the greatest prime factor is 37.

Answer: E

Scott Woodbury-Stewart
Founder and CEO
[email protected]

Image

See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews

ImageImage
Top
Join the discussion