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

It is currently 29 Aug 2014, 06:13

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

For some integer q, q^2 - 5 is divisible by all of the follo

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Expert Post
1 KUDOS received
Veritas Prep GMAT Instructor
User avatar
Joined: 16 Oct 2010
Posts: 4688
Location: Pune, India
Followers: 1081

Kudos [?]: 4862 [1] , given: 163

Re: q^2 - 5 [#permalink] New post 08 Jan 2011, 20:10
1
This post received
KUDOS
Expert's post
dimitri92 wrote:
For some integer q, q^2 - 5 is divisible by all of the following EXCEPT
(A) 29
(B) 30
(C) 31
(D) 38
(E) 41


The way I would approach this question:

So q^2 - 5 is divisible by all of the following except:
29, 31, 41 - big prime numbers, don't know any divisibility rules for these, forget them for the time being.. 38 = 19*2. (q^2 - 5) can be divisible by 2 (e.g. when q^2 ends with a 5, q^2 - 5 ends with a 0). As for 19, again a big prime number. Leave it for the time being.

(If the question is anywhere close to an actual GMAT question, they will not expect you to do many calculations with 29, 31, 41 etc. I see these big prime numbers and am quite convinced that they are just a smokescreen.Try and focus on what they could ask you like divisibility by 2, 3 etc. )

As for 30, q^2 - 5 is divisible by 10 (using the logic shown above). What about 3?
q^2 - 5 = q^2 - 1 - 4 = (q - 1)(q + 1) - 4
In any 3 consecutive numbers, (e.g. (q - 1), q, (q + 1)), one and only one number will be divisible by 3.
If either (q - 1) or (q + 1) is divisible by 3, (q - 1)(q + 1) is divisible by 3, which means (q - 1)(q + 1) - 4 cannot be divisible by 3. If q is divisible by 3, then q^2 will be divisible by 3 and q^2 - 5[/m] will not be divisible by 3.
_________________

Karishma
Veritas Prep | GMAT Instructor
My Blog

Save $100 on Veritas Prep GMAT Courses And Admissions Consulting
Enroll now. Pay later. Take advantage of Veritas Prep's flexible payment plan options.

Veritas Prep Reviews


Last edited by VeritasPrepKarishma on 08 Jan 2011, 20:17, edited 1 time in total.
Kaplan GMAT Prep Discount CodesKnewton GMAT Discount CodesManhattan GMAT Discount Codes
Expert Post
Veritas Prep GMAT Instructor
User avatar
Joined: 16 Oct 2010
Posts: 4688
Location: Pune, India
Followers: 1081

Kudos [?]: 4862 [0], given: 163

Re: q^2 - 5 [#permalink] New post 08 Jan 2011, 20:14
Expert's post
dimitri92: Didn't see your response since it was on page 2. But yes, that is exactly how I would think about it too. (Thought I think there is a small typo. You have a '+4' rather than a '-4')
_________________

Karishma
Veritas Prep | GMAT Instructor
My Blog

Save $100 on Veritas Prep GMAT Courses And Admissions Consulting
Enroll now. Pay later. Take advantage of Veritas Prep's flexible payment plan options.

Veritas Prep Reviews

SVP
SVP
User avatar
Joined: 09 Sep 2013
Posts: 2211
Followers: 185

Kudos [?]: 36 [0], given: 0

Premium Member
Re: For some integer q, q^2 - 5 is divisible by all of the follo [#permalink] New post 03 Oct 2013, 19:32
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.
_________________

GMAT Books | GMAT Club Tests | Best Prices on GMAT Courses | GMAT Mobile App | Math Resources | Verbal Resources

Re: For some integer q, q^2 - 5 is divisible by all of the follo   [#permalink] 03 Oct 2013, 19:32
    Similar topics Author Replies Last post
Similar
Topics:
2 Experts publish their posts in the topic If P is divisible by 2, is Q + 5 an integer? (1) The median maheshsrini 7 02 Oct 2011, 14:45
Is 0 divisable by all integers? amitjash 4 16 Oct 2010, 03:19
Are positive integers P , Q , and R equal? 1) P = Q 2) Q^2 = yuefei 6 14 Nov 2007, 14:47
Q2: By merging its two publishing divisions, the company nakib77 3 11 Nov 2005, 12:17
Display posts from previous: Sort by

For some integer q, q^2 - 5 is divisible by all of the follo

  Question banks Downloads My Bookmarks Reviews Important topics  

Go to page   Previous    1   2   [ 23 posts ] 



cron

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®.