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

It is currently 19 Oct 2014, 20:34

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 n= p^2-p+17, is n prime?

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
2 KUDOS received
VP
VP
User avatar
Status: Far, far away!
Joined: 02 Sep 2012
Posts: 1125
Location: Italy
Concentration: Finance, Entrepreneurship
GPA: 3.8
Followers: 113

Kudos [?]: 1190 [2] , given: 219

GMAT ToolKit User
If n= p^2-p+17, is n prime? [#permalink] New post 13 May 2013, 12:53
2
This post received
KUDOS
5
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

  95% (hard)

Question Stats:

30% (02:34) correct 70% (01:14) wrong based on 112 sessions
If n= p^2-p+17, is n prime?

1)p is prime

2)p is an integer less than 17


Hi guys this is a question I just created. OE here
As always any feedback is appreciated
[Reveal] Spoiler: OA

_________________

It is beyond a doubt that all our knowledge that begins with experience.

Kant , Critique of Pure Reason

Tips and tricks: Inequalities , Mixture | Review: MGMAT workshop
Strategy: SmartGMAT v1.0 | Questions: Verbal challenge SC I-II- CR New SC set out !! , My Quant

Rules for Posting in the Verbal Forum - Rules for Posting in the Quant Forum[/size][/color][/b]

Kaplan Promo CodeKnewton GMAT Discount CodesGMAT Pill GMAT Discount Codes
Manager
Manager
avatar
Joined: 11 Jun 2010
Posts: 84
Followers: 0

Kudos [?]: 9 [0], given: 17

Re: If n= p^2-p+17, is n prime? [#permalink] New post 13 May 2013, 18:00
N = p^2 - P + 17
N = P(P-1) + 17
Is N prime?

St1: P = Prime Number
if p = 2, 2*1 + 17 = 19 Prime
If p = 17, 17*16 + 17 = a multiple of 17. hence Not Prime
Insufficient

ST2: P = Integer < 17
True for all integers.
Product of any 2 consecutive integers + 17 will yield a prime number.
if p = 3, 3*2+17 = 23 (prime)
if p = 6, 6*5 + 17 = 47 (prime)
same for all integers less than 17.
SUFFICIENT

Ans B
2 KUDOS received
Senior Manager
Senior Manager
avatar
Joined: 21 Jan 2010
Posts: 348
Followers: 1

Kudos [?]: 74 [2] , given: 12

Re: If n= p^2-p+17, is n prime? [#permalink] New post 13 May 2013, 18:52
2
This post received
KUDOS
Zarrolou wrote:
If n= p^2-p+17, is n prime?

1)p is prime

2)p is an integer less than 17


Hi guys this is a question I just created. If you want give it a try: Kudos to the correct solution!
As always any feedback is appreciated



The correct answer is C.
A) If you pick p =17. Than n is not prime.
if you pick p=2. Than n is prime.
Insufficient.

B) From the above reasoning an integer less than 17 can be negative also.
If you take p=-17 than n is not prime. if you take p=2 than n is prime.

Hence , if you take both , then a prime number less than 17 will surely make n prime.

Hence, answer is C.
1 KUDOS received
Senior Manager
Senior Manager
avatar
Joined: 21 Jan 2010
Posts: 348
Followers: 1

Kudos [?]: 74 [1] , given: 12

Re: If n= p^2-p+17, is n prime? [#permalink] New post 13 May 2013, 18:53
1
This post received
KUDOS
srcc25anu wrote:
N = p^2 - P + 17
N = P(P-1) + 17
Is N prime?

St1: P = Prime Number
if p = 2, 2*1 + 17 = 19 Prime
If p = 17, 17*16 + 17 = a multiple of 17. hence Not Prime
Insufficient

ST2: P = Integer < 17
True for all integers.
Product of any 2 consecutive integers + 17 will yield a prime number.
if p = 3, 3*2+17 = 23 (prime)
if p = 6, 6*5 + 17 = 47 (prime)
same for all integers less than 17.
SUFFICIENT

Ans B


In B you are not considering negative numbers. If p=-17, than B is not sufficient.
1 KUDOS received
VP
VP
User avatar
Status: Far, far away!
Joined: 02 Sep 2012
Posts: 1125
Location: Italy
Concentration: Finance, Entrepreneurship
GPA: 3.8
Followers: 113

Kudos [?]: 1190 [1] , given: 219

GMAT ToolKit User
Re: If n= p^2-p+17, is n prime? [#permalink] New post 13 May 2013, 21:35
1
This post received
KUDOS
Well done Bluelagoon, you're correct!

Official Explanation

n=p^2-p+17

1)p is prime

if p = 17, then n=17^2-17+17= 17(17-1+1) is divisible by 17
if p=2 then n is prime.
Not sufficient

2)p is an integer less than 17

This seems to solve the problem because p cannot be 17. But now p can be -17, and we have a similar situation as above

if p= -17, then n=17*17+17+17=17(17+1+1) is divisible by 17
if p=2 then n is prime

1+2) Now we are sure that 17 or -17 is not an option, so the numbers will have no "common factor" and n will be prime
_________________

It is beyond a doubt that all our knowledge that begins with experience.

Kant , Critique of Pure Reason

Tips and tricks: Inequalities , Mixture | Review: MGMAT workshop
Strategy: SmartGMAT v1.0 | Questions: Verbal challenge SC I-II- CR New SC set out !! , My Quant

Rules for Posting in the Verbal Forum - Rules for Posting in the Quant Forum[/size][/color][/b]

CEO
CEO
User avatar
Joined: 09 Sep 2013
Posts: 2782
Followers: 206

Kudos [?]: 42 [0], given: 0

Premium Member
Re: If n= p^2-p+17, is n prime? [#permalink] New post 16 Jun 2014, 11:47
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

Manager
Manager
avatar
Joined: 04 Jan 2014
Posts: 128
Followers: 1

Kudos [?]: 5 [0], given: 24

Re: If n= p^2-p+17, is n prime? [#permalink] New post 17 Jun 2014, 02:37
I think the answer is E?

If p = 11 (prime), then p^2 - p + 17 = 121 - 11 + 17 = not prime.
Expert Post
Math Expert
User avatar
Joined: 02 Sep 2009
Posts: 23324
Followers: 3599

Kudos [?]: 28573 [0], given: 2803

Re: If n= p^2-p+17, is n prime? [#permalink] New post 17 Jun 2014, 02:39
Expert's post
Re: If n= p^2-p+17, is n prime?   [#permalink] 17 Jun 2014, 02:39
    Similar topics Author Replies Last post
Similar
Topics:
3 Experts publish their posts in the topic If n is a prime number and n ≠ 3, which of the following Jp27 8 03 Nov 2012, 00:49
2 Experts publish their posts in the topic If n is an integer, is n + 4 a prime number? metallicafan 6 18 Nov 2011, 09:15
4 Experts publish their posts in the topic If n is a whole number, is n + 1 a prime number? shekar123 2 01 Jun 2010, 18:44
If n is an integer, is n +2 a prime number? (1) n is a prime prude_sb 9 20 Aug 2006, 20:18
If n is an odd integer greater than 1, is n prime? (1) n is aravindrs 4 11 Dec 2005, 10:37
Display posts from previous: Sort by

If n= p^2-p+17, is n prime?

  Question banks Downloads My Bookmarks Reviews Important topics  


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®.