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

It is currently 22 Oct 2014, 06:34

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

How many prime factors does positive integer n have?

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Manager
Manager
avatar
Joined: 10 Feb 2011
Posts: 116
Followers: 1

Kudos [?]: 40 [0], given: 10

How many prime factors does positive integer n have? [#permalink] New post 29 Mar 2011, 11:30
00:00
A
B
C
D
E

Difficulty:

  85% (hard)

Question Stats:

28% (01:30) correct 72% (00:45) wrong based on 18 sessions
How many prime factors does positive integer n have?

(1) n/5 has only a prime factor.
(2) 3*n^2 has two different prime factors.
[Reveal] Spoiler: OA
Retired Moderator
User avatar
Joined: 02 Sep 2010
Posts: 807
Location: London
Followers: 76

Kudos [?]: 506 [0], given: 25

GMAT ToolKit User Reviews Badge
Re: How many prime factors does positive integer n have? [#permalink] New post 29 Mar 2011, 12:54
banksy wrote:
49. How many prime factors does positive integer n have?
(1) n/5 has only a prime factor.
(2) 3*n^2 has two different prime factors.



(1) : n/5 has one prime factor. So we know immediately that is a multiple of 5. Either n is of the form 5^k or 5x(another_prime)^k (Eg. n=125 or n=15 both work). Hence n has either 1 or 2 prime factors ... Insufficient

(2) : 3*n^2 has two factors. Again, n could have 1 or 2 factors. Eg n=15 OR n =125 both work

(1+2) : Take the case n = 15 and n = 125 ... both statements can be true together. Hence not clear if n has one prime factor or two


Hence, Answer is (e)
_________________

Math write-ups
1) Algebra-101 2) Sequences 3) Set combinatorics 4) 3-D geometry

My GMAT story

Get the best GMAT Prep Resources with GMAT Club Premium Membership

1 KUDOS received
SVP
SVP
avatar
Joined: 16 Nov 2010
Posts: 1691
Location: United States (IN)
Concentration: Strategy, Technology
Followers: 30

Kudos [?]: 298 [1] , given: 36

Premium Member Reviews Badge
Re: How many prime factors does positive integer n have? [#permalink] New post 29 Mar 2011, 17:00
1
This post received
KUDOS
(1) n/5 has one prime factor. So n could be 25 or 15, in which case n/5 = 5 or n/5 = 3, so n can have more than one prime factor. So Insufficient.

(2) 3*n^2 has two different prime factors. So if n = 5*3 = 15, or n = 5 or 25, then also the expression has two distinct prime factors. So Insufficient.

In (1) and (2), 15 can work, or 25 can work, so answer is E.
_________________

Formula of Life -> Achievement/Potential = k * Happiness (where k is a constant)

Get the best GMAT Prep Resources with GMAT Club Premium Membership

Re: How many prime factors does positive integer n have?   [#permalink] 29 Mar 2011, 17:00
    Similar topics Author Replies Last post
Similar
Topics:
How many prime factors does N have? shivanigs 7 06 Oct 2012, 00:31
How many prime factors does positive integer N have? (1) N/5 arjtryarjtry 10 04 Sep 2008, 02:18
How many prime factors does positive integer N have? (1) N/5 arjtryarjtry 8 28 Jul 2008, 01:33
How many prime divisors does positive integer N have? 1. 2N bmwhype2 3 08 Nov 2007, 20:17
How many prime divisors does positive integer N have? 1) 2N remgeo 10 16 May 2006, 07:13
Display posts from previous: Sort by

How many prime factors does positive integer n have?

  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®.