CR question

[This topic has 3 expert replies and 7 member replies]
Forum Index GMAT Verbal & Essays Critical Reasoning
Free $100 Amazon.com Gift Card - Buy a GMAT course using a Beat The GMAT discount code between Mar 8-22 and get a $100 Amazon.com Gift Card. Learn more!
Post New Topic   Post Reply

shahpuja
Just gettin' started!

Default Avatar

Joined: 23 Aug 2007
Posts: 2

Thanks given: 0
Thanked 0 times in 0 posts
Location: minneapolis
Topic: CR question
PostWed Mar 05, 2008 10:08 pm
Elapsed Time:
00:00
 Lap   Why a timer is critical to improving your score
28. (1) All A are B.
(2) Some B are C.
Which of the following is true?
(A) All A are C.
(B) No A are C.
(C) Some A are C.
(D) No C are A.
(E) None of the above.

I picked C. correct ans[color=white] E[/color]

please advise, my logic was that if a is part of b and some b is part of c, it is possible for some a to be part of C. why is that incorrect?
Back to top
View user's profile Send private message
ikant
Rising GMAT Star

Default Avatar

Joined: 05 Mar 2008
Posts: 62

Thanks given: 0
Thanked 5 times in 5 posts
Location: mumbai, India

Target GMAT Score: 750+
PostWed Mar 05, 2008 10:46 pm
Hello,

In such questions the most important point is to imagine a situation that encapsulates every possibility. You will see in the attached image the Venn Diagram that satisfies both the conditions and satisfies every possibility of interpretation.
Attachments
This post contains an attachment. You must be logged in to download/view this file. Please login or register as a user.

_________________
"To do is to be"
Back to top
View user's profile Send private message
Reply from GMAT/MBA Admissions Expert
See All Featured Experts
Stuart Kovinsky
GMAT Instructor

Most Active Expert Most Thanked Expert
Joined: 08 Jan 2008
Posts: 2263

Thanks given: 0
Thanked 541 times in 467 posts
Location: Toronto

GMAT Score: 800
PostWed Mar 05, 2008 11:48 pm
shahpuja wrote:
28. (1) All A are B.
(2) Some B are C.
Which of the following is true?
(A) All A are C.
(B) No A are C.
(C) Some A are C.
(D) No C are A.
(E) None of the above.

I picked C. correct ans E

please advise, my logic was that if a is part of b and some b is part of c, it is possible for some a to be part of C. why is that incorrect?
Venn diagrams are one way we can keep track of this type of information, although the diagram provided by ikant is actually NOT an accurate representation.

Let's examine the two rules we have:

(1) all A are B.

From this, we know that if something is A, it's also B.

(2) Some B are C.

From this, we know that there's at least one B that's also C.

If we put the two statements together, we don't know anything for sure. Could some A also be C? Sure, but it's not definite.

Let's use a real-life example to make that clear:

All Dogs are Mammals.

Some Mammals are Cats.

Does this mean that some dogs are cats? Of course not!

Going back to your point, it may just be that you misinterpreted the question.

"Which of the following IS true?" means that we're looking for something that MUST be true. In your own words, all that we can conclude is

Quote:
it is possible for some a to be part of C
which doesn't match what the question is asking.
_________________
Stuart Kovinsky, B.A. LL.B.
Academic Manager
Admissions Consultant
Kaplan Test Prep & Admissions
Toronto Office
1-800-KAP-TEST

GMAT Blogs

Learn more about me
Back to top
View user's profile Send private message
ikant
Rising GMAT Star

Default Avatar

Joined: 05 Mar 2008
Posts: 62

Thanks given: 0
Thanked 5 times in 5 posts
Location: mumbai, India

Target GMAT Score: 750+
PostThu Mar 06, 2008 1:48 am
Hi,

You are right..I just realised the mistake I did in drawing the diagram. There is actually no single Venn diagram possible to be drwan for this preposition.
_________________
"To do is to be"
Back to top
View user's profile Send private message
Kekela
Just gettin' started!

Default Avatar

Joined: 14 Jan 2008
Posts: 7

Thanks given: 0
Thanked 0 times in 0 posts

Test Date: 4 May
Target GMAT Score: >
PostMon Mar 10, 2008 3:17 am
...
Attachments
This post contains an attachment. You must be logged in to download/view this file. Please login or register as a user.
Back to top
View user's profile Send private message
rajmirra
Rising GMAT Star

Default Avatar

Joined: 08 Jan 2008
Posts: 65

Thanks given: 4
Thanked 3 times in 3 posts
Location: Canada
PostMon Mar 10, 2008 8:03 am
I dont remember this format of the question in any GMAT material. I have seen the question in IIM- CAT India. The question certainly is triggering you to think critically. But the real trick in GMAT is how you decipher the question and reach this stage (as stated in question). Has anyone seen this type of question in real GMAT?

Thanks.
~R
Back to top
View user's profile Send private message
michelsmithm
Rising GMAT Star

Default Avatar

Joined: 10 Mar 2008
Posts: 30

Thanks given: 0
Thanked 0 times in 0 posts
Location: Florida
PostFri Mar 28, 2008 4:00 am
No i have also not seen such questions i agree with rajmirra.
Back to top
View user's profile Send private message
Reply from GMAT/MBA Admissions Expert
See All Featured Experts
Stuart Kovinsky
GMAT Instructor

Most Active Expert Most Thanked Expert
Joined: 08 Jan 2008
Posts: 2263

Thanks given: 0
Thanked 541 times in 467 posts
Location: Toronto

GMAT Score: 800
PostFri Mar 28, 2008 10:19 am
This is much more of an LSAT style than GMAT style question. It's very rare for the GMAT to test you on formal logic.
_________________
Stuart Kovinsky, B.A. LL.B.
Academic Manager
Admissions Consultant
Kaplan Test Prep & Admissions
Toronto Office
1-800-KAP-TEST

GMAT Blogs

Learn more about me
Back to top
View user's profile Send private message
michelsmithm
Rising GMAT Star

Default Avatar

Joined: 10 Mar 2008
Posts: 30

Thanks given: 0
Thanked 0 times in 0 posts
Location: Florida
PostMon Mar 31, 2008 4:15 am
Thanks stuart for explanation but please provide some guidance where i can find such questions just for general practice. Question
Back to top
View user's profile Send private message
Reply from GMAT/MBA Admissions Expert
See All Featured Experts
Stuart Kovinsky
GMAT Instructor

Most Active Expert Most Thanked Expert
Joined: 08 Jan 2008
Posts: 2263

Thanks given: 0
Thanked 541 times in 467 posts
Location: Toronto

GMAT Score: 800
PostMon Mar 31, 2008 9:51 am
michelsmithm wrote:
Thanks stuart for explanation but please provide some guidance where i can find such questions just for general practice. Question
If you really want to practice this type of question (which is fairly rare on the GMAT), then I'd suggest LSAT materials which focus on the logical reasoning section of that test - especially inference questions.

If you want a better understanding of formal logic (and you only need to know the VERY basics, even for the LSAT), I'd look for a primer on if-then statements. The formal logic tested on the GMAT is minimal and even on the LSAT it's only what one would learn in the first week of a university level course.
_________________
Stuart Kovinsky, B.A. LL.B.
Academic Manager
Admissions Consultant
Kaplan Test Prep & Admissions
Toronto Office
1-800-KAP-TEST

GMAT Blogs

Learn more about me
Back to top
View user's profile Send private message
jamess
Rising GMAT Star

Default Avatar

Joined: 12 Apr 2008
Posts: 51

Thanks given: 0
Thanked 0 times in 0 posts
PostTue Apr 15, 2008 8:56 am
shahpuja wrote:
28. (1) All A are B.
(2) Some B are C.
Which of the following is true?
(A) All A are C.
(B) No A are C.
(C) Some A are C.
(D) No C are A.
(E) None of the above.

I picked C. correct ans E

please advise, my logic was that if a is part of b and some b is part of c, it is possible for some a to be part of C. why is that incorrect?
E is the correct answer.

You should draw a venn diagram to solve this type of question.

Here it is
_________________
Check out <a href="http://gmatadvice.blogspot.com">gmatadvice.blogspot.com</a> for useful tips to ace the GMAT.
<a href="http://gmatadvice.blogspot.com/2008/04/launched-ebook-on-critical-reasoning.html">ebook on critical reasoning</a> launched.
Back to top
View user's profile Send private message
Display posts from previous:   

Post New Topic   Post Reply All times are GMT - 7 Hours
Page 1 of 1
 
Forum Index GMAT Verbal & Essays Critical Reasoning
Most Active Members in Last 30 Days
1. harsh.champ 562 posts
2. shashank.ism 368 posts
3. thephoenix 319 posts
4. kstv 310 posts
5. ajith 279 posts
See More Top Beat The GMAT Members
Most Active Experts in Last 30 Days
1. lunarpower
Manhattan GMAT Teacher 		87 posts
2. Stuart Kovinsky
Kaplan GMAT Teacher 		63 posts
3. Lisa Anderson
Stacy Blackman Consulting 		54 posts
4. Testluv
Kaplan GMAT Teacher 		49 posts
5. Bryant@VeritasPrep
Veritas Prep 		41 posts
See More Top Beat The GMAT Experts