It is currently 14 Dec 2017, 14:57

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

Is a-3b an even number? 1). b=3a+3 2). b-a is an odd number

  post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
Manager
Manager
avatar
Joined: 04 Dec 2005
Posts: 81

Kudos [?]: 37 [0], given: 0

Is a-3b an even number? 1). b=3a+3 2). b-a is an odd number [#permalink]

Show Tags

New post 26 Sep 2006, 06:06
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 5 sessions

HideShow timer Statistics

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

Is a-3b an even number?
1). b=3a+3
2). b-a is an odd number

When the question description is like this without informing anything about whether a and b are integers or real numbers, how do we proceed. What does GMAT/OG say when nothing is given on what type of numbers we should use by default.

Solve the above problem and highlight below for the Question.

When a and b are integers you wil get the answer as D. However when you consider a and b as real numbers you will get a different answer. For ex: Try b=5 and a = 2, b = 3.5 and a = 1.5, your choice D fails.

Kudos [?]: 37 [0], given: 0

Current Student
User avatar
B
Joined: 29 Jan 2005
Posts: 5201

Kudos [?]: 440 [0], given: 0

 [#permalink]

Show Tags

New post 26 Sep 2006, 06:13
For a number to be even it has to be a integer, either pos or negative.

any integers chosen here result in a odd integer.

(D)

Kudos [?]: 440 [0], given: 0

1 KUDOS received
GMAT Instructor
avatar
Joined: 04 Jul 2006
Posts: 1259

Kudos [?]: 344 [1], given: 0

Location: Madrid
Re: DS- Even or Odd - Very important [#permalink]

Show Tags

New post 26 Sep 2006, 06:49
1
This post received
KUDOS
withme wrote:
Is a-3b an even number?
1). b=3a+3
2). b-a is an odd number




(1) a-3b=a-3(3a+3)= -8a-9 which may be even, odd, integer, non-integer, rational, irrational... NOTE THAT WE ARE NOT TOLD ABOUT THE PROPERTIES OF a. NOT SUFF

(2) b=(2k+1)+a where k is an integer

a-3b= a-3((2k+1)+a)= -2a -6k-3 NOT SUFF for the same reason


Together we see that -8a-9=-2a-6k-3 for some integer k

-6a=-6k+6=-6(k+1) => a=k+1

Thus a is an integer, either odd or even

(2) tells us that b is also an integer and that exactly one of {a,b} is even

If a is even and b is odd, a-3b is odd
If b is even and a is odd a-3b is odd

(1) and (2) combined tell us that a-3b is an odd number, not an even one
SUFF

Answer: C

Kudos [?]: 344 [1], given: 0

Manager
Manager
avatar
Joined: 12 Sep 2006
Posts: 91

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

 [#permalink]

Show Tags

New post 26 Sep 2006, 06:59
GMATT73 is right

only integers can be considered positive or negative. therefore the answer must be D

statement A:
b=3a+3
so 3a-b=-3, which is odd
that means a or b must be odd and the other even, so a-3b= odd
SUFF

statement B
b-a=odd
same as above, one of them must be odd and the other even, therefore a-3b=odd
SUFF

answer is D

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

Manager
Manager
avatar
Joined: 04 Dec 2005
Posts: 81

Kudos [?]: 37 [0], given: 0

 [#permalink]

Show Tags

New post 26 Sep 2006, 07:41
The question is asking to find whether a-3b is even but did not say anything on what should a and b can assume.

For example: take a = 0.5 and b = 3.5

which will give you a-3b = 0.5 - 10.5 = -10, an even number

Kudos [?]: 37 [0], given: 0

Non-Human User
User avatar
Joined: 09 Sep 2013
Posts: 14842

Kudos [?]: 287 [0], given: 0

Premium Member
Re: Is a-3b an even number? 1). b=3a+3 2). b-a is an odd number [#permalink]

Show Tags

New post 24 Aug 2017, 08:48
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________

GMAT Books | GMAT Club Tests | Best Prices on GMAT Courses | GMAT Mobile App | Math Resources | Verbal Resources

Kudos [?]: 287 [0], given: 0

Re: Is a-3b an even number? 1). b=3a+3 2). b-a is an odd number   [#permalink] 24 Aug 2017, 08:48
Display posts from previous: Sort by

Is a-3b an even number? 1). b=3a+3 2). b-a is an odd number

  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®.