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

 It is currently 18 Aug 2018, 21:13

### 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

# What is the sum of the first 100 positive odd numbers?

Author Message
TAGS:

### Hide Tags

Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 6028
GMAT 1: 760 Q51 V42
GPA: 3.82
What is the sum of the first 100 positive odd numbers?  [#permalink]

### Show Tags

25 Nov 2016, 02:26
00:00

Difficulty:

35% (medium)

Question Stats:

74% (00:52) correct 26% (01:17) wrong based on 150 sessions

### HideShow timer Statistics

What is the sum of the first 100 positive odd numbers?

A. 5,000 B. 7,500 C. 8,000 D. 10,000 E. 12,000

_________________

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 $99 for 3 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Intern Joined: 25 Oct 2016 Posts: 3 What is the sum of the first 100 positive odd numbers? [#permalink] ### Show Tags 25 Nov 2016, 02:48 1 This one is about pattern recognition. Set up a table as follows: Number Sum 1 1 3 4 5 9 7 16 9 25 Now as you see, the sum always equals the perfect square of the number of odd integers that you want to sum. So the sum of the first 5 odd integers is 5^2 = 25. The pattern continues. Thus, the sum of the first 100 odd integers will be equal to 100^2 = 10,000. The correct answer is (D). Current Student Joined: 28 Nov 2014 Posts: 887 Concentration: Strategy Schools: Fisher '19 (M) GPA: 3.71 Re: What is the sum of the first 100 positive odd numbers? [#permalink] ### Show Tags 25 Nov 2016, 03:44 3 For first n odd numbers, its n^2 and for first n even numbers, its n (n+1) Here, it'll be (100)^2 = 10000 Sent from my GT-N7100 using GMAT Club Forum mobile app CEO Joined: 12 Sep 2015 Posts: 2706 Location: Canada Re: What is the sum of the first 100 positive odd numbers? [#permalink] ### Show Tags 25 Nov 2016, 06:01 1 Top Contributor MathRevolution wrote: What is the sum of the first 100 positive odd numbers? A. 5,000 B. 7,500 C. 8,000 D. 10,000 E. 12,000 Before answering any GMAT quant problem, always check the answer choices first Here, the answer choices are somewhat spread apart, which means we can be somewhat aggressive in our estimations. Nice formula: 1 + 2 + 3 . . . + n = (n)(n + 1)/2 Let's use the above formula to find the sum of the first 200 integers (including odds AND evens) 1 + 2 + 3 . . . + 199 + 200 = (200)(200 + 1)/2 = (200)(201)/2 = (100)(201) = 20,100 So, the sum of the first 200 integers is 20,100 HALF of those integers are ODD and HALF are even. So, this sum includes the sum of the first 100 ODD integers and the sum of the first 100 EVEN integers. So, the sum of the first 100 ODD integers is APPROXIMATELY 20,100/2 20,100/2 = 10,050 So, the sum of the first 100 ODD integers ≈ 10,050 Answer choice D is the only one that's close to 10,050 so it must be the correct answer. RELATED VIDEO _________________ Brent Hanneson – Founder of gmatprepnow.com Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 6028 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: What is the sum of the first 100 positive odd numbers? [#permalink] ### Show Tags 28 Nov 2016, 01:41 ==> Since 1+3+5+….+(2n-1)=n 2, 1+3+…….(2*100-1)=100 2 =10,000 is derived. Hence, the answer is D. _________________ 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$99 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Intern
Joined: 15 Nov 2015
Posts: 26
Location: Netherlands
Schools: HEC Dec '17 (II)
GMAT 1: 730 Q47 V44
GPA: 3.99
Re: What is the sum of the first 100 positive odd numbers?  [#permalink]

### Show Tags

14 Dec 2016, 07:57
The sum of an arithmetic sequence equals (n(first term) + n(last term)/2)*n.

N1 = 1.
N 100 = N0 + (n-1)*2 = 1 + 198 = 199.

Now sum = ((1+199)/2)*100 = 100*100 = 10,000.
Senior Manager
Joined: 19 Apr 2016
Posts: 274
Location: India
GMAT 1: 570 Q48 V22
GMAT 2: 640 Q49 V28
GPA: 3.5
WE: Web Development (Computer Software)
Re: What is the sum of the first 100 positive odd numbers?  [#permalink]

### Show Tags

20 Jan 2017, 23:52
1
1
MathRevolution wrote:
What is the sum of the first 100 positive odd numbers?

A. 5,000 B. 7,500 C. 8,000 D. 10,000 E. 12,000

Sum of first n positive odd numbers = $$n^2$$

Therefore, Sum of first 100 positive odd numbers = $$100^2$$ = 10000;

Hence option D is correct.
Non-Human User
Joined: 09 Sep 2013
Posts: 7754
Re: What is the sum of the first 100 positive odd numbers?  [#permalink]

### Show Tags

19 Jul 2018, 21:56
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 sum of the first 100 positive odd numbers? &nbs [#permalink] 19 Jul 2018, 21:56
Display posts from previous: Sort by

# Events & Promotions

 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®.