if a and b are positive even integers, and the least common

Expert replies

airan: Master | Next Rank: 500 Posts; Posts: 127; Joined: Tue May 13, 2008 12:28 am; Thanked: 2 times; GMAT Score:710

by airan » Sat Jul 12, 2008 11:21 pm

If a and b are positive even integers, and the least common multiple of a and b is expressed as ab/n, which of the following statements could be false ?

1. n is a factor of both a and b
2. ab/n < ab

3. ab is multiple of 2.

4. ab/n is a multiple of 2.

5. n is a multiple of 4.

OA is 5

Last edited by airan on Mon Jul 14, 2008 12:50 am, edited 1 time in total.

Thanks
Airan

Like this post

Source: Beat The GMAT — Problem Solving | Sat Jul 12, 2008 11:21 pm

reachac: Legendary Member; Posts: 572; Joined: Fri Feb 22, 2008 9:25 am; Thanked: 21 times

by reachac » Sat Jul 12, 2008 11:32 pm

IMO E

Also in B I thot it should be <=

Like this post

swati.sug: Master | Next Rank: 500 Posts; Posts: 104; Joined: Wed Jun 04, 2008 4:04 pm; Thanked: 6 times

by swati.sug » Sat Jul 12, 2008 11:37 pm

My pick is 5......n is a multiple of 4 need not be true.
All others have to be true.

Like this post

vivekverma: Newbie | Next Rank: 10 Posts; Posts: 5; Joined: Wed Jan 23, 2008 11:38 am

by vivekverma » Sun Jul 13, 2008 1:14 am

Ans. E - n can be 2 as well...

Like this post

sudhir3127: Legendary Member; Posts: 829; Joined: Mon Jul 07, 2008 10:09 pmFollowed by: 3 members; Location: INDIA; Thanked: 84 times

by sudhir3127 » Sun Jul 13, 2008 2:58 am

Answer E.

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

Re: if a and b are positive even integers, and the least com

by Ian Stewart » Sun Jul 13, 2008 8:31 am

airan wrote:If a and b are positive even integers, and the least common multiple of a and b is expressed as ab/n, which of the following statements could be false ?

1. n is a factor of both a and b
2. ab/n < ab

3. ab is multiple of 2.

4. ab/n is a multiple of 2.

5. n is a multiple of 4.

This question is easier if you know that, for any positive integers a and b:

LCM(a,b) * GCD(a,b) = a*b

So LCM(a,b) = ab/GCD(a,b)

In this question, n is just the GCD of a and b. So we know automatically that n is a factor of a and b... A) must be true. If a and b are both even, they are both divisible by 2, so the smallest possible value for their GCD is 2. That is, n >= 2, so B) must be true (I'd add, in response to reachac's comment above, we do not need to have <= here). If a and b are even, ab is clearly even, and so is the LCM of a and b, so C) and D) must be true. E) is the only one that might be false; E will only be true if both a and b are divisible by 4.

For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

ianstewartgmat.com

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