GMATprep problem

This topic has expert replies
Junior | Next Rank: 30 Posts
Posts: 13
Joined: Fri Oct 17, 2008 3:06 am
Location: singapore

GMATprep problem

by sumatitandon » Fri Jan 09, 2009 3:05 am
The integers m and p are such that 2 < m< p , and m is not a factor of p, if r is the remainder , when p is divided by m , is r > 1?
1) The greatest common factor of m and p is 2
2) the least common factor of m and p is 30
Source: — Data Sufficiency |

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 2623
Joined: Mon Jun 02, 2008 3:17 am
Location: Montreal
Thanked: 1090 times
Followed by:355 members
GMAT Score:780

Re: GMATprep problem

by Ian Stewart » Fri Jan 09, 2009 6:40 am
sumatitandon wrote:The integers m and p are such that 2 < m< p , and m is not a factor of p, if r is the remainder , when p is divided by m , is r > 1?
1) The greatest common factor of m and p is 2
2) the least common factor of m and p is 30
If 1) is true, then m and p are both divisible by 2; in other words, m and p are both even. Whenever you divide one even number by another, the remainder must be even, so r cannot be 1. Since we're told r is not zero, then r must be greater than 1, and this statement is sufficient.

If 2) is true, it is still possible that r = 1. For example, we might have p = 6 and m = 5.

A.
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

Senior | Next Rank: 100 Posts
Posts: 35
Joined: Thu Nov 13, 2008 8:05 am
Thanked: 6 times

confused

by shulapa » Fri Jan 09, 2009 9:22 am
Hi,

I am confused :oops: . I think I miss understood your analysis of the second statement. I think I don't understand the difference between common factor and common multiple.
I thought that 30 is the "common multiple" of 5 and 6. Actually I cannot see how can 30 can be the "least common factor".

Can you please clarify on the difference between the two terms.

Thanks,

Legendary Member
Posts: 2467
Joined: Thu Aug 28, 2008 6:14 pm
Thanked: 331 times
Followed by:11 members

by cramya » Fri Jan 09, 2009 5:22 pm
Shulapa,
I think the 2nd statement should read least common multiple.

Regards,
Cramya

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 2623
Joined: Mon Jun 02, 2008 3:17 am
Location: Montreal
Thanked: 1090 times
Followed by:355 members
GMAT Score:780

by Ian Stewart » Fri Jan 09, 2009 5:31 pm
Yeah, I was remembering the problem from GMATPrep. The least common factor of two positive integers is always 1 - it could never be 30 - so the question doesn't make much sense as written in the original post. The original question reads 'least common multiple' in statement 2.
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

Legendary Member
Posts: 2467
Joined: Thu Aug 28, 2008 6:14 pm
Thanked: 331 times
Followed by:11 members

by cramya » Fri Jan 09, 2009 5:41 pm
Thanks Ian!

Junior | Next Rank: 30 Posts
Posts: 13
Joined: Fri Oct 17, 2008 3:06 am
Location: singapore

by sumatitandon » Fri Jan 09, 2009 6:21 pm
i m sorry.... stat 2 states lest common multiple.....

but why statement 2 is not sufficent ., i have tried other numbers also for ex: 3 and 10 the remainder is 1 again , so i feel that since remainder is 1 can't we conclude that r is not greater than 1 , pls explain where i m wrong......

Legendary Member
Posts: 2467
Joined: Thu Aug 28, 2008 6:14 pm
Thanked: 331 times
Followed by:11 members

by cramya » Fri Jan 09, 2009 6:33 pm
m=5 p=6

The remainder is 1 not greater than 1

m=10 p=15

remainder >1

When the remainder is equal to 1 we get NO (i.e if m was 5 and p 6)

When the remainder > 1 we get a YES

Hence stmt II is INSUFF (we cant say for sure)


P.S: IMO when the question is " Is something greater than something" the equalt to case and lesser than case would fall in the NO bucket.

When a question reads " Is something lesser than something" then the equal to case and greater than case would fall in the NO bucket

Ian, please correct me if I am mistaken here.

Hope this helps!

Regards,
Cramya

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 2623
Joined: Mon Jun 02, 2008 3:17 am
Location: Montreal
Thanked: 1090 times
Followed by:355 members
GMAT Score:780

by Ian Stewart » Fri Jan 09, 2009 11:45 pm
cramya wrote:
P.S: IMO when the question is " Is something greater than something" the equalt to case and lesser than case would fall in the NO bucket.

When a question reads " Is something lesser than something" then the equal to case and greater than case would fall in the NO bucket

Ian, please correct me if I am mistaken here.
Yes, that's exactly right.

Legendary Member
Posts: 2467
Joined: Thu Aug 28, 2008 6:14 pm
Thanked: 331 times
Followed by:11 members

by cramya » Fri Jan 09, 2009 11:58 pm
Thanks again Ian!!