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

 It is currently 15 Dec 2018, 01:39

### 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 December
PrevNext
SuMoTuWeThFrSa
2526272829301
2345678
9101112131415
16171819202122
23242526272829
303112345
Open Detailed Calendar
• ### Free GMAT Strategy Webinar

December 15, 2018

December 15, 2018

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.
• ### $450 Tuition Credit & Official CAT Packs FREE December 15, 2018 December 15, 2018 10:00 PM PST 11:00 PM PST Get the complete Official GMAT Exam Pack collection worth$100 with the 3 Month Pack ($299) # The Sum of first N consecutive odd integers is N^2. What is  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics Author Message TAGS: ### Hide Tags Manager Joined: 21 Jul 2006 Posts: 78 The Sum of first N consecutive odd integers is N^2. What is [#permalink] ### Show Tags 02 Aug 2006, 16:34 4 24 00:00 Difficulty: 55% (hard) Question Stats: 65% (02:07) correct 35% (02:17) wrong based on 605 sessions ### HideShow timer Statistics The Sum of first N consecutive odd integers is N^2. What is the sum of all odd integers between 13 and 39 inclusive. A. 351 B. 364 C. 410 D. 424 E. 450 Manager Joined: 25 Jul 2006 Posts: 96 ### Show Tags 02 Aug 2006, 16:40 B.... 1- 11 are the first 6 odd intergers; sum = 6^2 = 36 1- 39 are the first 20 odd intergers; sum = 400 sum of odd nos frm 13- 39 = 400-36 = 364 Manager Joined: 09 Apr 2006 Posts: 172 Location: Somewhere in Wisconsin! ### Show Tags 02 Aug 2006, 18:44 1 Use AP and you woudn't need the supplied formula: a(1) = 13; a(n) = a(1) + (n-1)d = 39 (where d =2). Sum = n/2[a(1) + a(n)] = 364, where n = 14 _________________ Thanks, Zooroopa SVP Joined: 30 Mar 2006 Posts: 1662 ### Show Tags 02 Aug 2006, 22:24 1 Number of odd numbers from 1-39 = 39+1/2 = 20 Sum = 400 Number of odd numbers between = 1-12 = (12 - 1 +1)/2 = 6 sum = 36 Sum between 13-39 inclusive = 400 - 36 = 364 Manager Joined: 26 Jun 2006 Posts: 151 ### Show Tags 03 Aug 2006, 08:03 I also used AP without using N^2 condition. For me, sometimes, it is easeir to just stick to basics and do the calcs. This way, at least, I know I will arrive at the correct answer sooner or later... Director Joined: 28 Dec 2005 Posts: 703 ### Show Tags 03 Aug 2006, 23:41 1 I would suggest using the formula, for the simple reason that instead of an AP the problem might refer to some fancy formula for an unknown sequence of numbers. Anyway here we go... For odd integers till 39, number of integers = 20 Sum = 20^2 = 400 For odd integers till (but not including 13), number of integers = 6 Sum = 6^2 = 36 Difference = 364 = B VP Joined: 29 Dec 2005 Posts: 1288 Re: PS : Number Prop. [#permalink] ### Show Tags 04 Aug 2006, 05:43 ghantark wrote: The Sum of first N consecutive odd integers is N^2. What is the sum of all odd integers between 13 and 39 inclusive. 351 364 410 424 450 OA later i never knew this formulea that sum of n consecutive odd integers = n^2. however, we can use regular formula: the sum of consecutive odd integers from 13-39 = n (L-s)/2 = [{(39-13)/2} +1][39-13] = 14 x 26 = 364 Manager Joined: 09 Apr 2006 Posts: 172 Location: Somewhere in Wisconsin! Re: PS : Number Prop. [#permalink] ### Show Tags 05 Aug 2006, 00:03 Professor wrote: ghantark wrote: The Sum of first N consecutive odd integers is N^2. What is the sum of all odd integers between 13 and 39 inclusive. 351 364 410 424 450 OA later i never knew this formulea that sum of n consecutive odd integers = n^2. however, we can use regular formula: the sum of consecutive odd integers from 13-39 = n (L-s)/2 = [{(39-13)/2} +1][39-13] = 14 x 26 = 364 It can be derived from the regular formula for A.P. 1+3+5+....=n/2[2.1+(n-1).2] = n^^2 !! _________________ Thanks, Zooroopa Manager Joined: 20 Mar 2006 Posts: 200 Re: PS : Number Prop. [#permalink] ### Show Tags 05 Aug 2006, 14:37 ghantark wrote: The Sum of first N consecutive odd integers is N^2. What is the sum of all odd integers between 13 and 39 inclusive. 351 364 410 424 450 OA later Sum of odd integers from 1 to 39 inclusive = 20^2=400 sum of odd integers from 1 to 11 inclusive = 6^2 = 36 therfore sum of odd integers between 13 and 39 incl = 400 -36 = 364 Hence B Heman Senior Manager Joined: 23 Oct 2010 Posts: 350 Location: Azerbaijan Concentration: Finance Schools: HEC '15 (A) GMAT 1: 690 Q47 V38 Re: The Sum of first N consecutive odd integers is N^2. What is [#permalink] ### Show Tags 07 Jun 2012, 00:58 1 I method - the sum of odd numbers till 39(inclusive) =n^2=20^2 the sum of odd numbers till 11 (inclusive) =n^2=6^2 20^2 -6^2=(20-6)(20+6)=26*14=364 ================ II method n* (a1+an)/2 n=((39-13)/2)+1=14 (39+13)/2* 14=26*14=364 _________________ Happy are those who dream dreams and are ready to pay the price to make them come true I am still on all gmat forums. msg me if you want to ask me smth Manager Status: Kitchener Joined: 03 Oct 2013 Posts: 89 Location: Canada Concentration: Finance, Finance GPA: 2.9 WE: Education (Education) Re: The Sum of first N consecutive odd integers is N^2. What is [#permalink] ### Show Tags 21 Jan 2015, 17:44 ghantark wrote: The Sum of first N consecutive odd integers is N^2. What is the sum of all odd integers between 13 and 39 inclusive. A. 351 B. 364 C. 410 D. 424 E. 450 from the question I see that it ask about the sum of odd numbers between 13 and 39 not from 13 to 39 therefore, 13 and 39 are not includes in the sum.So, there are 20 odd numbers from 1 to 39 so 20^2 = 400 and from 1 to 13 there are 7 odd numbers so it will be 7^2=49 400-49=351 if I am no right what will be the answer if the question was ask about the sum of odd numbers from 13 to 39 _________________ Click +1 Kudos if my post helped EMPOWERgmat Instructor Status: GMAT Assassin/Co-Founder Affiliations: EMPOWERgmat Joined: 19 Dec 2014 Posts: 13087 Location: United States (CA) GMAT 1: 800 Q51 V49 GRE 1: Q170 V170 Re: The Sum of first N consecutive odd integers is N^2. What is [#permalink] ### Show Tags 21 Jan 2015, 18:59 Hi All, These types of "sum of a sequence" questions can be approached in a number of different ways - you can use various formulas or you can approach this prompt by pattern-matching and minimizing the math that you have to do. For this question, you can use "bunching".... We're dealing with a sequence of CONSECUTIVE ODD INTEGERS: 13 to 39, inclusive. We're asked for the SUM of this group. 1) Start with the sum of the smallest and the biggest: 13 + 39 = 52 2) Now look at the 'next smallest' and the 'next biggest': 15 + 37 = 52 From this, you can see that you're just going to be adding up a bunch of 52s. We DO have to check to see if there's a "middle" term in this sequence that doesn't get "bunched" though. To determine if that middle term exists, we just have find the last few 52s in the group.... 21 and 31 23 and 29 25 and 27 Now we have proof that there is no middle term. We have 7 bunches of 52. 7(52) = 364 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!*****

SVP
Status: The Best Or Nothing
Joined: 27 Dec 2012
Posts: 1825
Location: India
Concentration: General Management, Technology
WE: Information Technology (Computer Software)
Re: The Sum of first N consecutive odd integers is N^2. What is  [#permalink]

### Show Tags

22 Jan 2015, 02:13
1
23a2012 wrote:
ghantark wrote:
The Sum of first N consecutive odd integers is N^2. What is the sum of all odd integers between 13 and 39 inclusive.

A. 351
B. 364
C. 410
D. 424
E. 450

from the question I see that it ask about the sum of odd numbers between 13 and 39 not from 13 to 39 therefore, 13 and 39 are not includes in the sum.So, there are 20 odd numbers from 1 to 39 so 20^2 = 400 and from 1 to 13 there are 7 odd numbers so it will be 7^2=49
400-49=351

if I am no right what will be the answer if the question was ask about the sum of odd numbers from 13 to 39

Its asking sum of odd integers between 13 and 39 inclusive, so we require to minus sum of odd integers up to 11 inclusive

$$= 20^2 - 6^2 = 26 * 14 = 364$$

_________________

Kindly press "+1 Kudos" to appreciate

Manager
Status: Kitchener
Joined: 03 Oct 2013
Posts: 89
Concentration: Finance, Finance
GPA: 2.9
WE: Education (Education)
Re: The Sum of first N consecutive odd integers is N^2. What is  [#permalink]

### Show Tags

22 Jan 2015, 15:23
ghantark wrote:
The Sum of first N consecutive odd integers is N^2. What is the sum of all odd integers between 13 and 39 inclusive.

A. 351
B. 364
C. 410
D. 424
E. 450

Thank you for EMPOWERgmatRichC and PareshGmat

But I still do not understand what will be the answer if the question was ask about the sum of odd numbers from 13 to

39 and why we do not includ 13?
_________________

Click +1 Kudos if my post helped

EMPOWERgmat Instructor
Status: GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 13087
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: Q170 V170
Re: The Sum of first N consecutive odd integers is N^2. What is  [#permalink]

### Show Tags

22 Jan 2015, 16:37
Hi 23a2012,

My explanation (and everyone else's too) includes 13 and 39 in the sum. The prompt uses the phrase "ALL odd integers between 13 and 39, INCLUSIVE." This means that we have to INCLUDE 13 and 39 and all of the explanations do that.

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!*****

Senior Manager
Joined: 23 Apr 2015
Posts: 305
Location: United States
WE: Engineering (Consulting)
Re: The Sum of first N consecutive odd integers is N^2. What is  [#permalink]

### Show Tags

23 Aug 2016, 20:27
ghantark wrote:
The Sum of first N consecutive odd integers is N^2. What is the sum of all odd integers between 13 and 39 inclusive.

A. 351
B. 364
C. 410
D. 424
E. 450

The numbers to be added are 13,15,...39. These are in Arithmetic progression with difference as 2.

a1 (first term) = 13
d = 2
N (number of terms)= $$\frac{(39-13)}{2} + 1 = 14$$
Sum = $$\frac{N}{2} *(2*a1 + (N-1)*d)$$
= $$\frac{14}{2} *(2*13 + (14-1)2)$$
= 364

+1 for Kudos
Intern
Joined: 30 Mar 2015
Posts: 10
Re: The Sum of first N consecutive odd integers is N^2. What is  [#permalink]

### Show Tags

18 Sep 2016, 10:54
what if the question was exlusive instead of inclusive ?
can you please show me the difference ?
I have tried to do it but i got confused should i remove 1 and 39 or just one of them
Thank you :D
Non-Human User
Joined: 09 Sep 2013
Posts: 9164
Re: The Sum of first N consecutive odd integers is N^2. What is  [#permalink]

### Show Tags

14 Jul 2018, 19:31
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: The Sum of first N consecutive odd integers is N^2. What is &nbs [#permalink] 14 Jul 2018, 19:31
Display posts from previous: Sort by