BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

LCF

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Master | Next Rank: 500 Posts
Posts: 265
Joined: Tue Jul 03, 2012 11:04 pm
Followed by:6 members

LCF

by grandh01 » Sat Sep 15, 2012 6:56 pm
What is the largest common factor of positive integers J & K

1) K=J + 1
2) kj is a multiple of 5

OA IS A
Top
Source: — Data Sufficiency |
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pm
Location: New York, NY
Thanked: 13060 times
Followed by:1906 members
GMAT Score:790

by GMATGuruNY » Sat Sep 15, 2012 7:07 pm
grandh01 wrote:What is the largest common factor of positive integers J & K

1) K=J + 1
2) kj is a multiple of 5

OA IS A
Statement 1: k = j+1
Since k is 1 more than j, j and k are CONSECUTIVE integers.
Consecutive integers are COPRIMES: they share no factors other than 1.
Thus, the greatest common factor of j and k is 1.
SUFFICIENT.

Statement 2: kj is a multiple of 5
If j=1 and k=5, the greatest common factor of j and k is 1.
If j=5 and k=5, the greatest common factor of j and k is 5.
Since the greatest common factor can be different values, INSUFFICIENT.

The correct answer is A.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Top
Master | Next Rank: 500 Posts
Posts: 435
Joined: Wed Nov 16, 2011 7:27 am
Thanked: 48 times
Followed by:16 members

by alex.gellatly » Sat Sep 15, 2012 7:12 pm
grandh01 wrote:What is the largest common factor of positive integers J & K

1) K=J + 1
2) kj is a multiple of 5
The question asks for the LCF between two integers J and K. Remember that the LCF is the largest factor which goes "into" two numbers. For example the LCF of 2 and 4 is 2 because both 2 and 4 have a 2 "inside"

Now to our statements:

STATEMENT 1: Sufficient. k=j+1 suggests that j and k are consecutive integers. Two consecutive integers LCF will simply be 1. You can find this out by testing numbers. If j=2, then k=3 LCF=1 J=10 k = 11 LCF is 1

STATEMENT 1: Insufficient. This does not tell us anything about j and k. It only says that one j or k is a multiple of 5 since jk together have a 5 "inside". We cannot determine the LCF.

The correct answer should be A
Hope this helps
A useful website I found that has every quant OG video explanation:

https://www.beatthegmat.com/useful-websi ... tml#475231
Top
Senior | Next Rank: 100 Posts
Posts: 48
Joined: Sat Jul 09, 2011 9:42 am

by ashg84 » Sun Sep 16, 2012 5:26 am
GMATGuruNY wrote:
grandh01 wrote:What is the largest common factor of positive integers J & K

1) K=J + 1
2) kj is a multiple of 5

OA IS A
Statement 1: k = j+1
Since k is 1 more than j, j and k are CONSECUTIVE integers.
Consecutive integers are COPRIMES: they share no factors other than 1.
Thus, the greatest common factor of j and k is 1.
SUFFICIENT.

Statement 2: kj is a multiple of 5
If j=1 and k=5, the greatest common factor of j and k is 1.
If j=5 and k=5, the greatest common factor of j and k is 5.
Since the greatest common factor can be different values, INSUFFICIENT.

The correct answer is A.
I have a doubt
Is the LCM of negative integers -1, -2 is 1
Top
Post new topic Post Reply
• Page 1 of 1