It is currently 18 Dec 2017, 06:58

Final Week of R1 Decisions:

CHAT Rooms | MIT Sloan | McCombs 


Close

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
Your Progress

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

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Close

Request Expert Reply

Confirm Cancel

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

x^2 + 5y = 49. is y an integer? 1. 1 < x < 4 2. x^2 is

  post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
Senior Manager
Senior Manager
avatar
Joined: 18 Jun 2007
Posts: 285

Kudos [?]: 66 [0], given: 0

x^2 + 5y = 49. is y an integer? 1. 1 < x < 4 2. x^2 is [#permalink]

Show Tags

New post 29 Sep 2008, 21:26
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions

HideShow timer Statistics

This topic is locked. If you want to discuss this question please re-post it in the respective forum.

x^2 + 5y = 49. is y an integer?

1. 1 < x < 4
2. x^2 is an integer

Please explain. OA to follow.

Kudos [?]: 66 [0], given: 0

SVP
SVP
avatar
Joined: 17 Jun 2008
Posts: 1530

Kudos [?]: 282 [0], given: 0

Re: DS: relation between x and x^2 [#permalink]

Show Tags

New post 29 Sep 2008, 21:39
E.

original equation can be translated to y = (49-x^2)/5.
In order for y to be an integer, numerator should either be 0 or a multiple of 5.

stmt1: insufficient. Take x = sqrt2, y is not an integer. Take x = 2, y is an integer.
stmt2: insufficient, for x^2 = 1, y is not an integer and for x^2 = 4, y is an integer.

Sombining 1 and 2, 1 < x^2 < 16.

Now, for x^2 = 4, y is an integer, for x^2 = 5, y is not an integer. Hence, insufficient.

Kudos [?]: 282 [0], given: 0

Intern
Intern
avatar
Joined: 15 Jun 2008
Posts: 17

Kudos [?]: 2 [0], given: 0

Location: Kiev, Ukraine
Schools: INSEAD
Re: DS: relation between x and x^2 [#permalink]

Show Tags

New post 30 Sep 2008, 01:37
I don't agree with E because from the first condition we know that 1<x<4 and from the second - that X^2 is an integer, which means that X is an integer as well. It means that X may be equal only to 2 or 3.

x^2+5y=49
5y=49-x^2
5y=(7-x)*(7+x)

If we substitute x with 2 or 3. we will get one multiplier 5 or 10, which means that (7-x)*(7+x) is divisible by 5, and in this case Y is an integer.

Kudos [?]: 2 [0], given: 0

1 KUDOS received
Senior Manager
Senior Manager
avatar
Joined: 18 Jun 2007
Posts: 285

Kudos [?]: 66 [1], given: 0

Re: DS: relation between x and x^2 [#permalink]

Show Tags

New post 30 Sep 2008, 02:03
1
This post received
KUDOS
nlutsenko wrote:
I don't agree with E because from the first condition we know that 1<x<4 and from the second - that X^2 is an integer, which means that X is an integer as well. It means that X may be equal only to 2 or 3.

x^2+5y=49
5y=49-x^2
5y=(7-x)*(7+x)

If we substitute x with 2 or 3. we will get one multiplier 5 or 10, which means that (7-x)*(7+x) is divisible by 5, and in this case Y is an integer.


nlutsenko, I made the same mistake cause i thought that if x^2 is an integer then x too has to be an integer. Reason: I could not think of a non integer number which can yield an integer when squared but that was a silly mistake on my part cause x can be 'root5' which will equal to '5' when squared.

This is a GMAT Prep2 question. Though I scored 740 with 9 mistakes in math section but 7 of them were such silly mistakes...this is the area of great concern for me...somehow my concentration is shakey. :beat

btw OA is E. thx scthakur

Kudos [?]: 66 [1], given: 0

Intern
Intern
avatar
Joined: 15 Jun 2008
Posts: 17

Kudos [?]: 2 [0], given: 0

Location: Kiev, Ukraine
Schools: INSEAD
Re: DS: relation between x and x^2 [#permalink]

Show Tags

New post 30 Sep 2008, 03:12
Thank you for explanation. I really didn't take into consideration square root of an integer. Thank again

Kudos [?]: 2 [0], given: 0

VP
VP
User avatar
Joined: 05 Jul 2008
Posts: 1402

Kudos [?]: 454 [0], given: 1

Re: DS: relation between x and x^2 [#permalink]

Show Tags

New post 30 Sep 2008, 20:19
rishi2377 wrote:
nlutsenko wrote:
I don't agree with E because from the first condition we know that 1<x<4 and from the second - that X^2 is an integer, which means that X is an integer as well. It means that X may be equal only to 2 or 3.

x^2+5y=49
5y=49-x^2
5y=(7-x)*(7+x)

If we substitute x with 2 or 3. we will get one multiplier 5 or 10, which means that (7-x)*(7+x) is divisible by 5, and in this case Y is an integer.


nlutsenko, I made the same mistake cause i thought that if x^2 is an integer then x too has to be an integer. Reason: I could not think of a non integer number which can yield an integer when squared but that was a silly mistake on my part cause x can be 'root5' which will equal to '5' when squared.

This is a GMAT Prep2 question. Though I scored 740 with 9 mistakes in math section but 7 of them were such silly mistakes...this is the area of great concern for me...somehow my concentration is shakey. :beat

btw OA is E. thx scthakur


Same mistake here. I was wondering why this its not C. The point we miss is x can be root 5 or root 8 and still be between 1 and 4.

I am slowly realizing one thing with all these number properties, inequalities. Bring all of them into one form such as x^2 here. I mean , the imp take away here is 1 < x < 4 means
1 < x^2 < 16 and the second one is x^2 is an integer. When we do the conversion we clearly see that x^2 can take the value of 2 through 15. other wise, we get trapped with 2 & 3.

Kudos [?]: 454 [0], given: 1

VP
VP
avatar
Joined: 17 Jun 2008
Posts: 1373

Kudos [?]: 437 [0], given: 0

Re: DS: relation between x and x^2 [#permalink]

Show Tags

New post 01 Oct 2008, 20:56
rishi2377 wrote:
x^2 + 5y = 49. is y an integer?

1. 1 < x < 4
2. x^2 is an integer

Please explain. OA to follow.

Clearly E
1) x=2,3,or any fraction too hence answer is different
2)x^2 can be 2,3,4,1,5,6 ... answer is different in each case !!!

combine both we get x=2,3,4,5,etc hence different answers
IMO E
_________________

cheers
Its Now Or Never

Kudos [?]: 437 [0], given: 0

Re: DS: relation between x and x^2   [#permalink] 01 Oct 2008, 20:56
Display posts from previous: Sort by

x^2 + 5y = 49. is y an integer? 1. 1 < x < 4 2. x^2 is

  post reply Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

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®.