• Board contributors include instructors with "800" GMAT scores.
  • 95% of posts have replies within 24 hours.
  • Join for discounts with 800score, VeritasPrep and ManhattanGMAT


FAQ  - Register  - Search - Login 

All times are UTC - 7 hours




Post new topic Reply to topic  [ 2 posts ] 
Author Message
 Post subject: average question
PostPosted: Tue Jul 07, 2009 8:29 pm 
Offline

Joined: Sun Jun 07, 2009 7:57 pm
Posts: 3
Question: If the average of 18 consecutive odd integers is 534, what is the least number in the set?

Ok so I know how to do this algebraically, you start with your odd variable which we will call X and then the next one will be X + 2, X + 4, etc until you have 18 terms. Then it will be 18X + 306/18 = 534 and then we can solve, but this method seems rather long. Is this the best way to solve this problem?


Top
 Profile  
 
 Post subject: Re: average question
PostPosted: Sun Jul 26, 2009 11:56 am 
Offline
User avatar

Joined: Mon Apr 06, 2009 5:44 pm
Posts: 81
There are three sum formulas that you should commit to memory:

1. Sum of the first n consecutive integers: n(n+1)/2

2. Sum of the first n consecutive even integers: n(n+1)

3. sum of the first n consecutive odd integers: n^2

So, back to the problem, we have: sum / number of odd integers = [n + (n+2) + (n+4) + ... + (n+34)] / 18 = 534. We can reduce this to 18n + (2 + 4 + 6 + ... + 34) / 18 = 9612 ==>
18n + (2+ 4 + ... + 34) = 173016. We can simplify the sum in the parenthesis using rule 2 from above: 17 x 18 = 306. So we have 18n + 306 / 18 = 534. And now you can solve in the usual way.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 2 posts ] 

All times are UTC - 7 hours


Who is online

Users browsing this forum: No registered users and 0 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group
Template made by DEVPPL -
phpBB SEO
 
GMAT(TM) and GMAT CAT (TM) are registered trademarks of the Graduate Management Admission Council(TM). The Graduate Management Admission Council(TM) does not endorse, nor is affiliated in any way with the owner or any content of this site.