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

 It is currently 23 Feb 2019, 07:55

### 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

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

## Events & Promotions

###### Events & Promotions in February
PrevNext
SuMoTuWeThFrSa
272829303112
3456789
10111213141516
17181920212223
242526272812
Open Detailed Calendar
• ### 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.
• ### 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

# What is the greatest prime factor of 1+2+3+。。。+40?

Author Message
TAGS:

### Hide Tags

Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6985
GMAT 1: 760 Q51 V42
GPA: 3.82
What is the greatest prime factor of 1+2+3+。。。+40?  [#permalink]

### Show Tags

Updated on: 19 Jun 2016, 17:06
00:00

Difficulty:

15% (low)

Question Stats:

81% (01:13) correct 19% (01:25) wrong based on 118 sessions

### HideShow timer Statistics

What is the greatest prime factor of 1+2+3+。。。+40?
A. 17
B. 29
C. 31
D. 37
E. 41

*An answer will be posted in 2 days.

_________________

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" Originally posted by MathRevolution on 17 Jun 2016, 23:27. Last edited by MathRevolution on 19 Jun 2016, 17:06, edited 1 time in total. Manager Joined: 18 Sep 2014 Posts: 227 Re: What is the greatest prime factor of 1+2+3+。。。+40? [#permalink] ### Show Tags 17 Jun 2016, 23:35 1 I dont understand this Sum = n(n+1)/2 Sum = 40*41/2 = 820 41 divides 820 evenly making E the answer. _________________ Kindly press the Kudos to appreciate my post !! Math Expert Joined: 02 Aug 2009 Posts: 7335 Re: What is the greatest prime factor of 1+2+3+。。。+40? [#permalink] ### Show Tags 18 Jun 2016, 00:05 MathRevolution wrote: What is the greatest prime factor of 1+2+3+。。。+40? A. 17 B. 29 C. 31 D. 37 E. 41 *An answer will be posted in 2 days. HI, find the sum from direct formula = n(n+1)/2 = 40(40+1)/2 = 20*41... 41 is a PRIME number, so ans is 41.. A is wrong ....E is the answer _________________ 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 4) Base while finding % increase and % decrease : https://gmatclub.com/forum/percentage-increase-decrease-what-should-be-the-denominator-287528.html GMAT Expert Board of Directors Status: QA & VA Forum Moderator Joined: 11 Jun 2011 Posts: 4391 Location: India GPA: 3.5 WE: Business Development (Commercial Banking) Re: What is the greatest prime factor of 1+2+3+。。。+40? [#permalink] ### Show Tags 18 Jun 2016, 00:15 With Chetan Answer must be (E) 41 Sume of the series is 820 Further $$820$$= $$2^2$$ x $$5^1$$ x $$41^1$$ So, 820 must be divisible by 41 which is the greatest prime factor of the series. MathRevolution Please recheck and confirm the correct answer... _________________ Thanks and Regards Abhishek.... PLEASE FOLLOW THE RULES FOR POSTING IN QA AND VA FORUM AND USE SEARCH FUNCTION BEFORE POSTING NEW QUESTIONS How to use Search Function in GMAT Club | Rules for Posting in QA forum | Writing Mathematical Formulas |Rules for Posting in VA forum | Request Expert's Reply ( VA Forum Only ) Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 6985 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: What is the greatest prime factor of 1+2+3+。。。+40? [#permalink] ### Show Tags 19 Jun 2016, 17:08 I am so sorry! I made a mistake, the correct answer is E. I will post the solution tomorrow! Thank you. _________________ 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"

Current Student
Joined: 03 Apr 2016
Posts: 80
Location: India
Concentration: Operations, General Management
GMAT 1: 720 Q50 V37
WE: Analyst (Computer Software)
Re: What is the greatest prime factor of 1+2+3+。。。+40?  [#permalink]

### Show Tags

19 Jun 2016, 22:30
Sum will be 41 * 20 , so greatest prime factor will be 41.

Sent from my SM-N910H using Tapatalk
Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6985
GMAT 1: 760 Q51 V42
GPA: 3.82
Re: What is the greatest prime factor of 1+2+3+。。。+40?  [#permalink]

### Show Tags

20 Jun 2016, 16:31
We can calculate 1+2+3+…..+n=n(n+1)/2. Then, 1+2+3+。。。+40=40(40+1)/2=20(41)=(2^2)(5)(41). Hence, the biggest prime factor is 41 and the correct answer is 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"

Current Student
Joined: 12 Aug 2015
Posts: 2621
Schools: Boston U '20 (M)
GRE 1: Q169 V154
Re: What is the greatest prime factor of 1+2+3+。。。+40?  [#permalink]

### Show Tags

22 Nov 2016, 01:03
Here N=> Sum of first 40 positive integers
N=40/2(1+40)
N=20*41
Clearly greatest Prime factor =41

Alternatively
Mean of an Ap series is the average of the first and the last term=(1+40)/2
Mena = 41/2
Sum/number of terms = mean
Sum = mean * 40
(41/2)*40 = N
N=20*41

Hence E
_________________
Manager
Status: Quant Expert Q51
Joined: 02 Aug 2014
Posts: 106
Re: What is the greatest prime factor of 1+2+3+。。。+40?  [#permalink]

### Show Tags

25 Nov 2016, 04:38
1+2+3+。。。+40= (41*40)/2=41*20

So the greatest prime factor is definitely 41

Best
_________________
Non-Human User
Joined: 09 Sep 2013
Posts: 9893
Re: What is the greatest prime factor of 1+2+3+。。。+40?  [#permalink]

### Show Tags

28 Jan 2019, 12:12
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________
Re: What is the greatest prime factor of 1+2+3+。。。+40?   [#permalink] 28 Jan 2019, 12:12
Display posts from previous: Sort by