It is currently 24 Nov 2017, 06:26

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# M25 #29

Author Message
Current Student
Joined: 26 Jun 2006
Posts: 124

Kudos [?]: 37 [4], given: 8

Schools: Ross Class of 2012
WE 1: Consumer Goods / IT
WE 2: Retail / Logistics

### Show Tags

09 Oct 2008, 07:34
4
KUDOS
2
This post was
BOOKMARKED
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

$$X$$ and $$Y$$ are prime integers. What is $$X + Y$$ ?

1. $$X - Y$$ is a prime integer
2. $$Y \lt X \lt 6$$

[Reveal] Spoiler: OA
E

Source: GMAT Club Tests - hardest GMAT questions

Is 1 considered a prime number? I selected C but was wrong. According to the answer:
S2 is not sufficient. Consider $$X = 5$$ , $$Y = 3$$ and $$X = 3$$ , $$Y = 2$$ which is true...

edit: but if you take both together... the only possible answer is X=5 and Y=3 and not X=3 and Y=2. The only way S2 and S1 is not sufficient is if we consider 1 a prime number... am I missing something?

Kudos [?]: 37 [4], given: 8

Senior Manager
Joined: 04 Jan 2006
Posts: 276

Kudos [?]: 44 [5], given: 0

### Show Tags

09 Oct 2008, 09:56
5
KUDOS
sharmar wrote:
$$X$$ and $$Y$$ are prime integers. What is $$X + Y$$ ?

1. $$X - Y$$ is a prime integer
2. $$Y \lt X \lt 6$$

(C) 2008 GMAT Club - m25#29

* Statement (1) ALONE is sufficient, but Statement (2) ALONE is not sufficient
* Statement (2) ALONE is sufficient, but Statement (1) ALONE is not sufficient
* BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient
* EACH statement ALONE is sufficient
* Statements (1) and (2) TOGETHER are NOT sufficient

Is 1 considered a prime number? I selected C but was wrong. According to the answer:
S2 is not sufficient. Consider $$X = 5$$ , $$Y = 3$$ and $$X = 3$$ , $$Y = 2$$ which is true...

edit: but if you take both together... the only possible answer is X=5 and Y=3 and not X=3 and Y=2. The only way S2 and S1 is not sufficient is if we consider 1 a prime number... am I missing something?

1) X - Y is prime
case 1: 5 - 2 = 3
5 + 2 = 7

case 2: 7 - 5 = 2
7 + 5 = 13

2) Y < X < 6
Possible value for Y = {2, 3}
Possible value for X = {3, 5}

1) & 2)
Case 1: 2 < 3 < 6
3 - 2 = 1 ----- Not Prime
Drop this case

Case 2: 2 < 5 < 6
5 - 2 = 3 ----- Prime
5 + 2 = 7

Case 3: 3 < 5 < 6
5 - 3 = 2 ----- Prime
5 + 3 = 8

Kudos [?]: 44 [5], given: 0

Retired Moderator
Joined: 05 Jul 2006
Posts: 1749

Kudos [?]: 445 [1], given: 49

### Show Tags

09 Oct 2008, 10:11
1
KUDOS
[quote="sharmar"]$$X$$ and $$Y$$ are prime integers. What is $$X + Y$$ ?

1. $$X - Y$$ is a prime integer
2. $$Y \lt X \lt 6$$

the difference between consecutive primes = /2/ except 2,3 = /1/

from 1

x,y could be any prime >3....insuff

from 2

obviously not suff

both

no idea if they are consec or not ...insuff

Kudos [?]: 445 [1], given: 49

SVP
Joined: 29 Aug 2007
Posts: 2471

Kudos [?]: 857 [1], given: 19

### Show Tags

09 Oct 2008, 11:14
1
KUDOS
sharmar wrote:
Nevermind... I think I figured it out... I didn't consider 5-2 = 3

ALSO CONSIDER 7-2 = 5 OR 7-5 = 2

SOME MORE 13 - 2 = 11 AND 13 - 2 = 11
_________________

Gmat: http://gmatclub.com/forum/everything-you-need-to-prepare-for-the-gmat-revised-77983.html

GT

Kudos [?]: 857 [1], given: 19

Intern
Joined: 30 Dec 2009
Posts: 1

Kudos [?]: 1 [1], given: 0

### Show Tags

02 Jul 2010, 06:05
1
KUDOS
No, 1 is not considered a prime. A prime number (or a prime) is a natural number that has exactly two distinct natural number divisors: 1 and itself.

Posted from my mobile device

Kudos [?]: 1 [1], given: 0

Intern
Joined: 29 Mar 2010
Posts: 16

Kudos [?]: 7 [1], given: 0

Schools: UCLA, USC
WE 1: 3 Yr at leading SAAS company

### Show Tags

05 Jul 2010, 20:53
1
KUDOS
1
This post was
BOOKMARKED
X and Y are prime integers. What is X+Y ?

1. X-Y is a prime integer
2. Y<X<6

Case 1: X-Y is prime number
Set (X,Y) : (5,2), (5,3),(7,2),(7,5),(13,2)(13,11).
No Unique Soln.

Case 2. Y<X<6
Set (X,Y) : (5,3),(5,2)(3,2)
No Unique Soln.

Combining Case 1 & Case 2 : no Unique Soln.

Thus E: Stmt 1 & Stmt 2 Together are not sufficient.

Kudos [?]: 7 [1], given: 0

Math Expert
Joined: 02 Sep 2009
Posts: 42356

Kudos [?]: 133204 [1], given: 12439

### Show Tags

27 Mar 2012, 02:09
1
KUDOS
Expert's post
sharmar wrote:
$$X$$ and $$Y$$ are prime integers. What is $$X + Y$$ ?

1. $$X - Y$$ is a prime integer
2. $$Y \lt X \lt 6$$

[Reveal] Spoiler: OA
E

Source: GMAT Club Tests - hardest GMAT questions

Is 1 considered a prime number? I selected C but was wrong. According to the answer:
S2 is not sufficient. Consider $$X = 5$$ , $$Y = 3$$ and $$X = 3$$ , $$Y = 2$$ which is true...

edit: but if you take both together... the only possible answer is X=5 and Y=3 and not X=3 and Y=2. The only way S2 and S1 is not sufficient is if we consider 1 a prime number... am I missing something?

If $$x$$ and $$y$$ are prime numbers, what is the value of $$x+y$$ ?

(1) $$x-y$$ is a prime number --> if $$x=5$$ and $$y=2$$ (notice that in this case $$x-y=3=prime$$) then $$x+y=7$$ but if $$x=5$$ and $$y=3$$ (notice that in this case $$x-y=2=prime$$) then $$x+y=8$$. Not sufficient.

(2) $$y<x<6$$ --> the same example as above is valid for this statement also. Not sufficient.

(1)+(2) Again, the example from statement (1) is still valid and gives two different values for $$x+y$$. Not sufficient.

_________________

Kudos [?]: 133204 [1], given: 12439

Math Expert
Joined: 02 Sep 2009
Posts: 42356

Kudos [?]: 133204 [1], given: 12439

### Show Tags

10 Jul 2013, 06:13
1
KUDOS
Expert's post
knightofdelta wrote:
Bunuel wrote:
sharmar wrote:
$$X$$ and $$Y$$ are prime integers. What is $$X + Y$$ ?

1. $$X - Y$$ is a prime integer
2. $$Y \lt X \lt 6$$

[Reveal] Spoiler: OA
E

Source: GMAT Club Tests - hardest GMAT questions

Is 1 considered a prime number? I selected C but was wrong. According to the answer:
S2 is not sufficient. Consider $$X = 5$$ , $$Y = 3$$ and $$X = 3$$ , $$Y = 2$$ which is true...

edit: but if you take both together... the only possible answer is X=5 and Y=3 and not X=3 and Y=2. The only way S2 and S1 is not sufficient is if we consider 1 a prime number... am I missing something?

If $$x$$ and $$y$$ are prime numbers, what is the value of $$x+y$$ ?

(1) $$x-y$$ is a prime number --> if $$x=5$$ and $$y=2$$ (notice that in this case $$x-y=3=prime$$) then $$x+y=7$$ but if $$x=5$$ and $$y=3$$ (notice that in this case $$x-y=2=prime$$) then $$x+y=8$$. Not sufficient.

(2) $$y<x<6$$ --> the same example as above is valid for this statement also. Not sufficient.

(1)+(2) Again, the example from statement (1) is still valid and gives two different values for $$x+y$$. Not sufficient.

Can we also consider negative cases of these integers, since the question did not explicitly state that the integers were positive?

No, we cannot. "If $$x$$ and $$y$$ are prime numbers..." Only positive numbers can be primes.

Hope it helps.
_________________

Kudos [?]: 133204 [1], given: 12439

Manager
Joined: 29 Jun 2010
Posts: 246

Kudos [?]: 50 [0], given: 12

Schools: LBS, Oxford

### Show Tags

02 Jul 2010, 05:19
isnt 1 a prime number ?

Kudos [?]: 50 [0], given: 12

Manager
Status: On...
Joined: 16 Jan 2011
Posts: 184

Kudos [?]: 71 [0], given: 62

### Show Tags

06 Jul 2011, 14:38
1 simple question : are negative prime numbers considered in GMAT ?

If yes, this question can be solved in 30 sec....else the 3,2 explanation is correct
_________________

Labor cost for typing this post >= Labor cost for pushing the Kudos Button
http://gmatclub.com/forum/kudos-what-are-they-and-why-we-have-them-94812.html

Kudos [?]: 71 [0], given: 62

Director
Joined: 21 Dec 2009
Posts: 582

Kudos [?]: 844 [0], given: 20

Concentration: Entrepreneurship, Finance

### Show Tags

14 Jul 2011, 08:30
Prime number is an integer number P$$>=$$2, divisible by only itself and 1.
_________________

KUDOS me if you feel my contribution has helped you.

Kudos [?]: 844 [0], given: 20

Senior Manager
Joined: 19 Oct 2010
Posts: 252

Kudos [?]: 91 [0], given: 27

Location: India
GMAT 1: 560 Q36 V31
GPA: 3

### Show Tags

30 Jul 2011, 00:44
Some folks here say 1 is not a prime. But it is.
_________________

petrifiedbutstanding

Kudos [?]: 91 [0], given: 27

Math Expert
Joined: 02 Sep 2009
Posts: 42356

Kudos [?]: 133204 [0], given: 12439

### Show Tags

27 Mar 2012, 04:18
petrifiedbutstanding wrote:
Some folks here say 1 is not a prime. But it is.

1 is DEFINITELY not a prime number. The smallest prime is 2.

For more on Number Properties check: math-number-theory-88376.html

Hope it helps.
_________________

Kudos [?]: 133204 [0], given: 12439

Intern
Joined: 21 May 2012
Posts: 1

Kudos [?]: [0], given: 0

### Show Tags

11 Jul 2012, 23:17
Question can be answered by using both the statements together

x=5
y=3
x-y=2 which is a prime number

and yes 1 is not prime..

Kudos [?]: [0], given: 0

Manager
Joined: 14 Jun 2012
Posts: 64

Kudos [?]: 16 [0], given: 1

### Show Tags

31 Aug 2012, 21:08
Good question. I am particularly happy that I did end up solving this one is about a min and half.

Followed the plugging in of values approach with values as 5,2,3 for statement (ii) and for statement (i) there are a whole number of possible options.

Both statements together as well fail to give a concrete answer for the values 2,3,5. Hence chose E.
_________________

My attempt to capture my B-School Journey in a Blog : tranquilnomadgmat.blogspot.com

There are no shortcuts to any place worth going.

Kudos [?]: 16 [0], given: 1

Manager
Joined: 02 May 2012
Posts: 108

Kudos [?]: 75 [0], given: 34

Location: United Kingdom
WE: Account Management (Other)

### Show Tags

18 Sep 2012, 06:16
Picking up on bunnels statement re: 1 being a prime....

If you have trouble remembering in the heat of battle, think: a prime number has 2 factors, 1 and itself. Although 1 has factors of 1 and iteslf, these are one and the same and therefore it doesn't have 2 (intiger) factors.
_________________

In the study cave!

Kudos [?]: 75 [0], given: 34

Manager
Joined: 13 Dec 2012
Posts: 194

Kudos [?]: 110 [0], given: 29

### Show Tags

10 Jul 2013, 05:11
Bunuel wrote:
sharmar wrote:
$$X$$ and $$Y$$ are prime integers. What is $$X + Y$$ ?

1. $$X - Y$$ is a prime integer
2. $$Y \lt X \lt 6$$

[Reveal] Spoiler: OA
E

Source: GMAT Club Tests - hardest GMAT questions

Is 1 considered a prime number? I selected C but was wrong. According to the answer:
S2 is not sufficient. Consider $$X = 5$$ , $$Y = 3$$ and $$X = 3$$ , $$Y = 2$$ which is true...

edit: but if you take both together... the only possible answer is X=5 and Y=3 and not X=3 and Y=2. The only way S2 and S1 is not sufficient is if we consider 1 a prime number... am I missing something?

If $$x$$ and $$y$$ are prime numbers, what is the value of $$x+y$$ ?

(1) $$x-y$$ is a prime number --> if $$x=5$$ and $$y=2$$ (notice that in this case $$x-y=3=prime$$) then $$x+y=7$$ but if $$x=5$$ and $$y=3$$ (notice that in this case $$x-y=2=prime$$) then $$x+y=8$$. Not sufficient.

(2) $$y<x<6$$ --> the same example as above is valid for this statement also. Not sufficient.

(1)+(2) Again, the example from statement (1) is still valid and gives two different values for $$x+y$$. Not sufficient.

Can we also consider negative cases of these integers, since the question did not explicitly state that the integers were positive?
_________________

Blog: The MBA Journey of an African Doctor

Blog updated: July 27, 2014

Kudos [?]: 110 [0], given: 29

Intern
Joined: 10 Jun 2013
Posts: 7

Kudos [?]: [0], given: 7

### Show Tags

10 Jul 2013, 07:25
petrifiedbutstanding wrote:
Some folks here say 1 is not a prime. But it is.

Natural numbers that have EXACTLY two factors are called prime numbers. Obviously, the number "1" has exactly 1 factor, so it is neither prime nor composite.. Yeah, this number is a different breed !!
_________________

GMAT ATTACKK!!

Kudos [?]: [0], given: 7

Manager
Joined: 13 Dec 2012
Posts: 194

Kudos [?]: 110 [0], given: 29

### Show Tags

10 Jul 2013, 07:27
heartbeats1987 wrote:
petrifiedbutstanding wrote:
Some folks here say 1 is not a prime. But it is.

Natural numbers that have EXACTLY two factors are called prime numbers. Obviously, the number "1" has exactly 1 factor, so it is neither prime nor composite.. Yeah, this number is a different breed !!

Right. So if I see "different breed" on a GMAT DS, I should think "1" right?
_________________

Blog: The MBA Journey of an African Doctor

Blog updated: July 27, 2014

Kudos [?]: 110 [0], given: 29

Math Expert
Joined: 02 Sep 2009
Posts: 42356

Kudos [?]: 133204 [0], given: 12439

### Show Tags

10 Jul 2013, 07:30
knightofdelta wrote:
heartbeats1987 wrote:
petrifiedbutstanding wrote:
Some folks here say 1 is not a prime. But it is.

Natural numbers that have EXACTLY two factors are called prime numbers. Obviously, the number "1" has exactly 1 factor, so it is neither prime nor composite.. Yeah, this number is a different breed !!

Right. So if I see "different breed" on a GMAT DS, I should think "1" right?

1 is NOT a prime number. The smallest prime is 2. And this is not only for the GMAT but generally.

For more check Number Theory chapter of our Math Book: math-number-theory-88376.html

Hope it helps.
_________________

Kudos [?]: 133204 [0], given: 12439

Re: M25 #29   [#permalink] 10 Jul 2013, 07:30

Go to page    1   2    Next  [ 24 posts ]

Display posts from previous: Sort by

# M25 #29

Moderator: Bunuel

 Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.