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

Redeem

Prime DS

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
User avatar
Legendary Member
Posts: 1665
Joined: Thu Nov 03, 2011 7:04 pm
Thanked: 165 times
Followed by:70 members

Prime DS

by karthikpandian19 » Thu Dec 15, 2011 7:13 pm
If y ≠ 3 and 3x/y is a prime integer greater than 2, which of the following must be true?
â… . x = y
â…¡. y = 1
â…¢. x and y are prime integers.

(A) None
(B) â…  only
(C) â…¡only
(D) â…¢only
(E) â… and â…¢
Top
Source: — Problem Solving |

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 3835
Joined: Fri Apr 02, 2010 10:00 pm
Location: Milpitas, CA
Thanked: 1854 times
Followed by:523 members
GMAT Score:770

by Anurag@Gurome » Thu Dec 15, 2011 8:38 pm
karthikpandian19 wrote:If y ≠ 3 and 3x/y is a prime integer greater than 2, which of the following must be true?
â… . x = y
â…¡. y = 1
â…¢. x and y are prime integers.

(A) None
(B) â…  only
(C) â…¡only
(D) â…¢only
(E) â… and â…¢
(I) x = y
If x = 5, y = 5, then 3x/y = 3 (a prime) greater than 2.
If x = 25, y = 15, then 3x/y = 5 (a prime number) greater than 2.
So, x = y is not always true.

(II) y = 1 is again not always true.

(III) x and y are prime integers is again not true because if we take x = 10, y = 6, then 3x/y = 5
So, again it is not true always.

The correct answer is A.
Last edited by Anurag@Gurome on Fri Dec 16, 2011 3:30 am, edited 1 time in total.
Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)

Join Our Facebook Groups
GMAT with Gurome
https://www.facebook.com/groups/272466352793633/
Admissions with Gurome
https://www.facebook.com/groups/461459690536574/
Career Advising with Gurome
https://www.facebook.com/groups/360435787349781/
Top
User avatar
Legendary Member
Posts: 1665
Joined: Thu Nov 03, 2011 7:04 pm
Thanked: 165 times
Followed by:70 members

by karthikpandian19 » Thu Dec 15, 2011 10:35 pm
In your proving portion, you had considered "I" y=3, but as per the statement y"not equal to" 3?????
Anurag@Gurome wrote:
karthikpandian19 wrote:If y ≠ 3 and 3x/y is a prime integer greater than 2, which of the following must be true?
â… . x = y
â…¡. y = 1
â…¢. x and y are prime integers.

(A) None
(B) â…  only
(C) â…¡only
(D) â…¢only
(E) â… and â…¢
(I) x = y
If x = 5, y = 5, then 3x/y = 3 (a prime) greater than 2.
If x = 7, y = 3, then 3x/y = 7 (a prime number) greater than 2.
So, x = y is not always true.

(II) y = 1 is again not always true.

(III) x and y are prime integers is again not true because if we take x = 10, y = 6, then 3x/y = 5
So, again it is not true always.

The correct answer is A.
Top
Senior | Next Rank: 100 Posts
Posts: 49
Joined: Thu Feb 17, 2011 1:36 am
Thanked: 8 times
Followed by:2 members

by ankush123251 » Fri Dec 16, 2011 3:06 am
@ Anurag@Gurome:
Correct me if i am wrong:In your proof firstly you took y = 3 but in question its clearly given y is not 3.
Secondly you took it under x=y,and x=7,y=3?? if x= 7 and x= y how can y be 3.

I believe the answer is A.
Since x = y always results in 3x/y being 3 which is greater than 2 and prime integer.
B)y =1 leads to 3x which depends on value of x,hence not true.
C)X and Y being prime integers leads to 3x/y not being prime integer.
Thus A.
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 3835
Joined: Fri Apr 02, 2010 10:00 pm
Location: Milpitas, CA
Thanked: 1854 times
Followed by:523 members
GMAT Score:770

by Anurag@Gurome » Fri Dec 16, 2011 3:31 am
ankush123251 wrote:@ Anurag@Gurome:
Correct me if i am wrong:In your proof firstly you took y = 3 but in question its clearly given y is not 3.
Secondly you took it under x=y,and x=7,y=3?? if x= 7 and x= y how can y be 3.

I believe the answer is A.
Since x = y always results in 3x/y being 3 which is greater than 2 and prime integer.
B)y =1 leads to 3x which depends on value of x,hence not true.
C)X and Y being prime integers leads to 3x/y not being prime integer.
Thus A.
My mistake, i have edited the previous reply. Thanks for pointing it out.
Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)

Join Our Facebook Groups
GMAT with Gurome
https://www.facebook.com/groups/272466352793633/
Admissions with Gurome
https://www.facebook.com/groups/461459690536574/
Career Advising with Gurome
https://www.facebook.com/groups/360435787349781/
Top
Senior | Next Rank: 100 Posts
Posts: 49
Joined: Thu Feb 17, 2011 1:36 am
Thanked: 8 times
Followed by:2 members

by ankush123251 » Fri Dec 16, 2011 3:38 am
Is the answer None?
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 3835
Joined: Fri Apr 02, 2010 10:00 pm
Location: Milpitas, CA
Thanked: 1854 times
Followed by:523 members
GMAT Score:770

by Anurag@Gurome » Fri Dec 16, 2011 3:43 am
ankush123251 wrote:Is the answer None?
Yes, that's right, it's none.
Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)

Join Our Facebook Groups
GMAT with Gurome
https://www.facebook.com/groups/272466352793633/
Admissions with Gurome
https://www.facebook.com/groups/461459690536574/
Career Advising with Gurome
https://www.facebook.com/groups/360435787349781/
Top
Post new topic Post Reply
• Page 1 of 1