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

Redeem

If x and y are positive integers, and 1 is the greatest

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Legendary Member
Posts: 1622
Joined: Thu Mar 01, 2018 7:22 am
Followed by:2 members

If x and y are positive integers, and 1 is the greatest

by Gmat_mission » Sat Mar 17, 2018 8:54 am
If x and y are positive integers, and 1 is the greatest common divisor of x and y, what is the greatest common divisor of 2x and 3y?

A. 1
B. Cannot be determined
C. 2
D. 5
E. 6

[spoiler]OA=B[/spoiler].

Since the greatest common divisor or 2 and 3 is 1, it shouldn't be A the answer? I got confused. Experts, I'd appreciate your help here. Thanks.
Top
Source: — Problem Solving |

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 16207
Joined: Mon Dec 08, 2008 6:26 pm
Location: Vancouver, BC
Thanked: 5254 times
Followed by:1268 members
GMAT Score:770

by Brent@GMATPrepNow » Sat Mar 17, 2018 4:49 pm
Gmat_mission wrote:If x and y are positive integers, and 1 is the greatest common divisor of x and y, what is the greatest common divisor of 2x and 3y?

A. 1
B. Cannot be determined
C. 2
D. 5
E. 6
Consider these two cases.

case 1: x = 3 and y = 2. This satisfies the condition that 1 is the greatest common divisor of x and y
In this case 2x = 2(3) = 6, and 3y = 3(2) = 6
So, the greatest common divisor of 2x and 3y is 6

case 2: x = 1 and y = 1. This satisfies the condition that 1 is the greatest common divisor of x and y
In this case 2x = 2(1) = 2, and 3y = 3(1) = 3
So, the greatest common divisor of 2x and 3y is 1

Answer: B

Cheers
Brent
Brent Hanneson - Creator of GMATPrepNow.com
Image
Top
User avatar
GMAT Instructor
Posts: 1462
Joined: Thu Apr 09, 2015 9:34 am
Location: New York, NY
Thanked: 39 times
Followed by:22 members

by Jeff@TargetTestPrep » Thu Mar 22, 2018 2:54 pm
Gmat_mission wrote:If x and y are positive integers, and 1 is the greatest common divisor of x and y, what is the greatest common divisor of 2x and 3y?

A. 1
B. Cannot be determined
C. 2
D. 5
E. 6

If x = 3 and y = 2, then 2x = 6 and 3y = 6, and their greatest common divisor is 6.

However, if x = 5 and y = 6, then 2x = 10 and 3y = 18, and their greatest common divisor is 2.

Answer: B

Jeffrey Miller
Head of GMAT Instruction
[email protected]

Image

See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 2095
Joined: Tue Dec 04, 2012 3:22 pm
Thanked: 1443 times
Followed by:247 members

by ceilidh.erickson » Fri Mar 23, 2018 8:34 am
Gmat_mission wrote:If x and y are positive integers, and 1 is the greatest common divisor of x and y, what is the greatest common divisor of 2x and 3y?

A. 1
B. Cannot be determined
C. 2
D. 5
E. 6

[spoiler]OA=B[/spoiler].

Since the greatest common divisor or 2 and 3 is 1, it shouldn't be A the answer? I got confused. Experts, I'd appreciate your help here. Thanks.
Here's a general rule: if you see "cannot be determined" in PS answer choices, ask yourself - can I think of different cases that would both fit the given information? Can I try to DISPROVE? Brent showed exactly how to do so on this problem.

Here's another example: https://www.beatthegmat.com/ratio-of-tw ... 86618.html
Ceilidh Erickson
EdM in Mind, Brain, and Education
Harvard Graduate School of Education
Top
Post new topic Post Reply
• Page 1 of 1