Even-Odd

Expert replies

gmattester: Master | Next Rank: 500 Posts; Posts: 172; Joined: Wed Oct 31, 2007 11:21 am; Thanked: 1 times

by gmattester » Thu Aug 21, 2008 8:50 pm

IS the integer n odd?
1) n is divisible by 3.
2) 2n is divisible by twice as many positive integers as n

First stmt is clear to me, Can someone explain the 2nd one.

Like this post

Source: Beat The GMAT — Data Sufficiency | Thu Aug 21, 2008 8:50 pm

P_mashru: Senior | Next Rank: 100 Posts; Posts: 43; Joined: Wed Jun 11, 2008 5:03 am; Location: Mumbai; GMAT Score:530

by P_mashru » Thu Aug 21, 2008 9:49 pm

to understand B clearly, assure two different value sets for n and then arrive on 2n

let me try;
Assume n as Odd - let's say 5, divisible by 2 different integers (factors); 1 & 5
so 2n is 10 - having 4 factors; 1,2,5,10

Now Assure even - let's say 6 - 4 factors; 1,2,3,6
so 2n is 12 - 6 factors; 1,2,3,4,6,12

Tried with couple of other odd and even nos and found the same result.

IMO B

What is OA?

I am I

Like this post

robust: Newbie | Next Rank: 10 Posts; Posts: 1; Joined: Sun Jun 29, 2008 11:02 am

by robust » Thu Aug 21, 2008 10:36 pm

i think this is B because to have twice the number of factors if multiplied by 2, n has to have factors which are distinct and prime (not including 2)

meaning that it will be odd since all prime numbers other than 2 are odd.

Like this post

gmattester: Master | Next Rank: 500 Posts; Posts: 172; Joined: Wed Oct 31, 2007 11:21 am; Thanked: 1 times

by gmattester » Thu Aug 21, 2008 10:48 pm

robust wrote:i think this is B because to have twice the number of factors if multiplied by 2, n has to have factors which are distinct and prime (not including 2)

meaning that it will be odd since all prime numbers other than 2 are odd.

OA is B but can you explain.
I am not clear how you proved that n has to have factors which are distinct and prime

Like this post

GMAT/MBA Expert

Ian Stewart: GMAT Instructor; Posts: 2623; Joined: Mon Jun 02, 2008 3:17 amFollowed by: 355 members; Location: Montreal; Thanked: 1090 times; GMAT Score:780

by Ian Stewart » Fri Aug 22, 2008 5:14 am

Ron Purewal posted a good explanation of the reason here:

www.beatthegmat.com/few-quetions-which- ... 10004.html

Like this post

vish150783: Senior | Next Rank: 100 Posts; Posts: 58; Joined: Sun Jun 17, 2007 8:24 am

by vish150783 » Fri Aug 22, 2008 7:21 am

I tried using a table for the second seems to help gather my ideas quite clearly..

n 2n nf 2nf
3 6 2 4
4 8 3 4
5 10 2 4
9 18 3 6

here nf = factors of n
2nf - factors of 2n

you see a pattern emerges. only for odd numbers it seems true.[/list]

Like this post

gmattester: Master | Next Rank: 500 Posts; Posts: 172; Joined: Wed Oct 31, 2007 11:21 am; Thanked: 1 times

by gmattester » Fri Aug 22, 2008 10:32 am

vish150783 wrote:I tried using a table for the second seems to help gather my ideas quite clearly..

n 2n nf 2nf
3 6 2 4
4 8 3 4
5 10 2 4
9 18 3 6

here nf = factors of n
2nf - factors of 2n

you see a pattern emerges. only for odd numbers it seems true.[/list]

I am not clear how you have calculated nf and 2nf and what pattern emerges

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

560 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review