• FREE GMAT Exam
Know how you'd score today for $0 Available with Beat the GMAT members only code • 1 Hour Free BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • Free Practice Test & Review How would you score if you took the GMAT Available with Beat the GMAT members only code • Free Veritas GMAT Class Experience Lesson 1 Live Free Available with Beat the GMAT members only code • Award-winning private GMAT tutoring Register now and save up to$200

Available with Beat the GMAT members only code

• Magoosh
Study with Magoosh GMAT prep

Available with Beat the GMAT members only code

• 5-Day Free Trial
5-day free, full-access trial TTP Quant

Available with Beat the GMAT members only code

• Get 300+ Practice Questions

Available with Beat the GMAT members only code

• Free Trial & Practice Exam
BEAT THE GMAT EXCLUSIVE

Available with Beat the GMAT members only code

• 5 Day FREE Trial
Study Smarter, Not Harder

Available with Beat the GMAT members only code

## Greatest common divisor

tagged by: Brent@GMATPrepNow

This topic has 2 expert replies and 0 member replies
j_shreyans Legendary Member
Joined
07 Aug 2014
Posted:
510 messages
Followed by:
5 members
3

#### Greatest common divisor

Wed Oct 22, 2014 8:18 am
If x and y are positive integers, which of the following CANNOT be the greatest common divisor of 35x and 20y?

A)5

B)5(x - y)

C)20x

D)20y

E)35x

OAC

### GMAT/MBA Expert

GMATGuruNY GMAT Instructor
Joined
25 May 2010
Posted:
14182 messages
Followed by:
1820 members
13060
GMAT Score:
790
Wed Oct 22, 2014 9:42 am
j_shreyans wrote:
If x and y are positive integers, which of the following CANNOT be the greatest common divisor of 35x and 20y?

A)5

B)5(x - y)

C)20x

D)20y

E)35x
C: 20x
Dividing 35x by 20x, we get:
35x/20x = 7/4.
Since 35x/20x = non-integer, 20x is not a factor of 35x.
Thus, it is not possible for 20x to be the greatest common divisor of 35x and 20y.

_________________
Mitch Hunt
GMAT Private Tutor
GMATGuruNY@gmail.com
If you find one of my posts helpful, please take a moment to click on the "UPVOTE" icon.
Available for tutoring in NYC and long-distance.

Free GMAT Practice Test How can you improve your test score if you don't know your baseline score? Take a free online practice exam. Get started on achieving your dream score today! Sign up now.

### GMAT/MBA Expert

Brent@GMATPrepNow GMAT Instructor
Joined
08 Dec 2008
Posted:
11517 messages
Followed by:
1229 members
5254
GMAT Score:
770
Wed Oct 22, 2014 9:46 am
Quote:
If x and y are positive integers, which of the following CANNOT be the greatest common divisor of 35x and 20y?

A) 5
B) 5(x - y)
C) 20x
D) 20y
E) 35x
The wording of the question tells us that 4 of the answer choices CAN be the greatest common divisor (GCD) of 35x and 20y, and one of them cannot.

So, might BEGIN by eliminating those answer choices that CAN be the greatest common divisor of 35x and 20y

A) 5
5 is a DIVISOR of both 35x and 20y, but can it be the GCD of 35x and 20y?
YES. If x = 1 and y = 1, then 5 is the GCD of 35x and 20y.
ELIMINATE A

B) 5(x - y)
CAN 5(x - y) be the GCD of 35x and 20y?
YES. If x = 3 and y = 2, then 5(x - y) = 5, 35x = 105 and 20y = 40
Since 5 is the GCD of 105 and 40, we can ELIMINATE B

Aside: It can be tough finding values such that 4 of the answer choices are, indeed, the GCD of 35x and 20y. So, we should also be looking for another approach that shows that an answer choice CANNOT be the GCD of 35x and 20y

C) 20x
CAN 20x be the GCD of 35x and 20y?
NO!
How do we know this?
20x cannot be the greatest common DIVISOR of 35x and 20y, because 20x isn't even a DIVISOR of 35x
Notice that 35x/20x = 35/20 = 7/4
This tells us that 20x cannot be a DIVISOR of 35x, which means 20x cannot be the GCD of 35x and 20y.

Cheers,
Brent

_________________
Brent Hanneson â€“ Founder of GMATPrepNow.com
Use our video course along with

Check out the online reviews of our course
Come see all of our free resources

GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMATâ€™s FREE 60-Day Study Guide and reach your target score in 2 months!

### Top First Responders*

1 GMATGuruNY 69 first replies
2 Rich.C@EMPOWERgma... 41 first replies
3 Brent@GMATPrepNow 40 first replies
4 Jay@ManhattanReview 24 first replies
5 Terry@ThePrinceto... 10 first replies
* Only counts replies to topics started in last 30 days
See More Top Beat The GMAT Members

### Most Active Experts

1 GMATGuruNY

The Princeton Review Teacher

134 posts
2 Jeff@TargetTestPrep

Target Test Prep

111 posts
3 Rich.C@EMPOWERgma...

EMPOWERgmat

111 posts
4 Scott@TargetTestPrep

Target Test Prep

103 posts
5 Max@Math Revolution

Math Revolution

92 posts
See More Top Beat The GMAT Experts