Find all School-related info fast with the new School-Specific MBA Forum

It is currently 23 Oct 2014, 12:04

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.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

If the sum of the first n positive integers is S , what is

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
VP
VP
avatar
Joined: 30 Sep 2004
Posts: 1493
Location: Germany
Followers: 4

Kudos [?]: 52 [0], given: 0

If the sum of the first n positive integers is S , what is [#permalink] New post 29 Nov 2004, 06:25
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions
If the sum of the first n positive integers is S , what is the sum of the first n positive even integers, in terms of S ?

(A) S/2
(B) S
(C) 2S
(D) 2S + 2
(E) 4S

can someone pls explain ???
Intern
Intern
avatar
Joined: 14 Oct 2004
Posts: 27
Followers: 0

Kudos [?]: 0 [0], given: 0

Pick Numbers [#permalink] New post 29 Nov 2004, 06:48
The answer is C.

First postive integers can be 1, 2, S = 3
First even positive integers will be 2,4, so sum will be S * 2
_________________

Victory always starts in the head. It's a state of mind

Manager
Manager
avatar
Joined: 09 Sep 2004
Posts: 166
Followers: 1

Kudos [?]: 1 [0], given: 0

 [#permalink] New post 29 Nov 2004, 07:11
Yep the ans is C

I picked numbers. I feel that is the easiest way.

Let n = 3

S will be 6 (1+2+3)

For the n first even integers:

2+4+6 = 12. Therefore S is now 2S. You can try other numbers and you will always get 2S as ur answer.

Hope this helps :wink:

Last edited by ninomoi on 29 Nov 2004, 09:32, edited 1 time in total.
Director
Director
User avatar
Joined: 21 Sep 2004
Posts: 619
Followers: 1

Kudos [?]: 5 [0], given: 0

 [#permalink] New post 29 Nov 2004, 07:25
sum of first n positive integers is n(n+1)/2...

sum of first n even positive integers is n(n+1) which is 2S
how I arrived at n(n+1)

=2+4+6+......+2n
=2[1+2+3......+n]
=2[n(n+1)/2]
=n(n+1)
=2S

answer is C
Director
Director
User avatar
Joined: 07 Nov 2004
Posts: 697
Followers: 4

Kudos [?]: 19 [0], given: 0

 [#permalink] New post 29 Nov 2004, 11:22
I get C as well.

Sum of 1st n numbers S = n(n+1)/2

Sum of 1st n even numbers
= (n(4+(n-1)2))/2 (Using Arithmetic progression formula)
= n(n+1)
= 2S
Manager
Manager
User avatar
Joined: 31 Aug 2004
Posts: 169
Location: Vancouver, BC, Canada
Followers: 1

Kudos [?]: 4 [0], given: 0

 [#permalink] New post 29 Nov 2004, 12:18
Mmm...why do we assume these n numbers are consecutive positive integers? What if they are in a random sequence like 1,2,5,8,13?
Manager
Manager
avatar
Joined: 09 Sep 2004
Posts: 166
Followers: 1

Kudos [?]: 1 [0], given: 0

Re: PS - 13 [#permalink] New post 29 Nov 2004, 12:38
christoph wrote:
If the sum of the first n positive integers is S , what is the sum of the first n positive even integers, in terms of S ?



The question asks for the first n +ve integers. n could 3 which means 1,2,3
Manager
Manager
avatar
Joined: 09 Sep 2004
Posts: 166
Followers: 1

Kudos [?]: 1 [0], given: 0

Re: PS - 13 [#permalink] New post 29 Nov 2004, 12:38
christoph wrote:
If the sum of the first n positive integers is S , what is the sum of the first n positive even integers, in terms of S ?



Junino

The question asks for the first n +ve integers. n could be = 3 which means 1,2,3 or n=5 which will be 1,2,3,4,5
Manager
Manager
avatar
Joined: 30 Jul 2004
Posts: 102
Followers: 1

Kudos [?]: 0 [0], given: 0

 [#permalink] New post 29 Nov 2004, 14:29
gayathri - What is the formula to calculate the SUM of n numbers in an Arithmetic Progression.
Director
Director
User avatar
Joined: 07 Nov 2004
Posts: 697
Followers: 4

Kudos [?]: 19 [0], given: 0

 [#permalink] New post 29 Nov 2004, 15:36
gmat+obsessed wrote:
gayathri - What is the formula to calculate the SUM of n numbers in an Arithmetic Progression.


Sum of "n" numbers in an AP = (n/2)[2a+(n-1)d]
where
a = 1st number in the series
d = difference between consecutive terms in the series
Manager
Manager
User avatar
Joined: 31 Aug 2004
Posts: 169
Location: Vancouver, BC, Canada
Followers: 1

Kudos [?]: 4 [0], given: 0

 [#permalink] New post 30 Nov 2004, 14:59
ninomoi, thanks for your explanation!
:-D
  [#permalink] 30 Nov 2004, 14:59
    Similar topics Author Replies Last post
Similar
Topics:
If the sum of the first n positive integers is S, what is lan583 3 05 Oct 2006, 12:03
If S is the sum of the first n positive integers, what is amansingla4 6 02 May 2006, 03:56
If S is the sum of the first n positive integers, what is john2005 7 10 Apr 2006, 19:12
If S is the sum of the first n positive integers, what is gmat_crack 10 08 Apr 2006, 21:09
If S is the sum of the first n positive integers, what is celiaXDN 2 01 Feb 2006, 09:11
Display posts from previous: Sort by

If the sum of the first n positive integers is S , what is

  Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Privacy Policy| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group and phpBB SEO

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®.