Events & Promotions
|
|
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
Track
Your Progress
Practice
Pays
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Apr 2301:30 AM EDT
-02:30 AM EDT
Struggling with GMAT Verbal as a non-native speaker? Harsh improved his score from 595 to 695 in just 45 days—and scored a 99 %ile in Verbal (V88)! Learn how smart strategy, clarity, and guided prep helped him gain 100 points.
Apr 2212:30 AM EDT
-01:30 AM EDT
At one point, she believed GMAT wasn’t for her. After scoring 595, self-doubt crept in and she questioned her potential. But instead of quitting, she made the right strategic changes. The result? A remarkable comeback to 695. Check out how Saakshi did it.
Apr 2308:00 PM PDT
-09:00 PM PDT
Video explanations + diagnosis of 10 weakest areas + 150+ short videos + study plan!
Apr 2610:00 AM EDT
-11:00 AM EDT
The Target Test Prep course represents a quantum leap forward in GMAT preparation, a radical reinterpretation of the way that students should study. Try before you buy with a 5-day, full-access trial of the course for FREE!
Apr 2711:00 AM EDT
-12:00 PM EDT
Prefer video-based learning? The Target Test Prep OnDemand course is a one-of-a-kind video masterclass featuring 400 hours of lecture-style teaching by Scott Woodbury-Stewart, founder of Target Test Prep and one of the most accomplished GMAT instructors
Apr 2808:00 AM PDT
-11:00 AM PDT
Whether you are just beginning your MBA journey or fine-tuning your path to a 700+ score, GMAT Day is designed to give you a competitive edge.
N
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
(N/A)
Question Stats:
22% (00:06) correct
78%
(00:02)
wrong
based on 17
sessions
History
Date
Time
Result
Not Attempted Yet
Since we have been working on some logical reasoning questions I'm going to try to collect the principles I'm following here for everybody's reference. Please feel free to discuss and add more. 
If X then Y
This is the equivalent of: If non Y then non X.
Example: If it rains, then I will take an umbrella with me. I don't have a umbrella with me. That must mean it is not raining.
This is NOT equivalent to: If Y then X, or If Y then non X, or if non Y then X. In fact, if we know "If X then Y" and Y occurred, X may or may not happen.
Example. If it rains, then I will definitely take an umbrella with me. I have a umbrella with me today. Is it raining? It may or may not be raining. I said if it rains I will take an umbralla with me. But I could also take an umbralla with me just for the sake of it, even if it doesn't rain. By the same token, if it is not raining, do I have an umbralla with me? I may or may not have.
Using symbals:
X->Y<nonY>nonX
These two below are the same thing:
nonX->Y<nonY>X
X->nonY <Y>non X
Y if and only if X
This is the equivalent of: If X then Y, AND if Y then X. Also, if non X then non Y. If non Y then non X.
Example:
I will take an umbralla with me if and only if it rains. If it rains, then I have the umbralla with me. If I have the umbralla, then it must be raining. If I don't have the umbralla, then it mustn't be raining. If it isn't raining, then I don't have the umbralla with me.
Y unless X
This is the equivalent of: If non X then Y. Also, if non Y then X.
Example:
I will take an umbralla with me unless it is sunny. If it is not sunny, I will take an umbralla with me. If I don't have an umbralla with me, it must mean that it is sunny. However, if it is sunny, I may or may not take an umbralla with me. If I have my umbralla with me, it may or may not be sunny.
If X then Y
This is the equivalent of: If non Y then non X.
Example: If it rains, then I will take an umbrella with me. I don't have a umbrella with me. That must mean it is not raining.
This is NOT equivalent to: If Y then X, or If Y then non X, or if non Y then X. In fact, if we know "If X then Y" and Y occurred, X may or may not happen.
Example. If it rains, then I will definitely take an umbrella with me. I have a umbrella with me today. Is it raining? It may or may not be raining. I said if it rains I will take an umbralla with me. But I could also take an umbralla with me just for the sake of it, even if it doesn't rain. By the same token, if it is not raining, do I have an umbralla with me? I may or may not have.
Using symbals:
X->Y<nonY>nonX
These two below are the same thing:
nonX->Y<nonY>X
X->nonY <Y>non X
Y if and only if X
This is the equivalent of: If X then Y, AND if Y then X. Also, if non X then non Y. If non Y then non X.
Example:
I will take an umbralla with me if and only if it rains. If it rains, then I have the umbralla with me. If I have the umbralla, then it must be raining. If I don't have the umbralla, then it mustn't be raining. If it isn't raining, then I don't have the umbralla with me.
Y unless X
This is the equivalent of: If non X then Y. Also, if non Y then X.
Example:
I will take an umbralla with me unless it is sunny. If it is not sunny, I will take an umbralla with me. If I don't have an umbralla with me, it must mean that it is sunny. However, if it is sunny, I may or may not take an umbralla with me. If I have my umbralla with me, it may or may not be sunny.
03 Mar 2005, 11:19
Kudos
Bookmarks
Necessary conditions:
If A is a necessary condition of B, that means A must happen for B to happen. In other words, if B happened, A must be true. If A is not true, then B can't happen.
In summary: If B then A. If non A then non B.
Example: I will take my umbralla with me only if it rains.
Raining is a necessary condition for my taking the umbralla with me.
If it is not raining, you can be sure that I don't have my umbralla with me.
Sufficient conditions:
If A is a sufficient condition of B, that means if A happens B must happen. In other words, if B did not happen, A must be false.
In summary: If A then B. If non B then non A.
Example: I will take my umbralla with me if it rains.
Raining is a sufficient condition for me to take the umbralla with me.
If it is not raining, you are not sure whether I have my umbralla with me. But if I don't have my umbralla with me, you can be sure that it is not raining.
Necessary and sufficient
If A is a necessary and sufficient condition for B, that means if A happen B must happen, and if A does not happen, B does not happen. In other words, A=B. It is equivalent with B if and only if A.
In summary: If A then B. If B then A. If non B then non A. If non A then non B.
Example: I will take my umbralla if and only if it rains.
If it is raining, you can be sure I have the umbralla. If it is not raining, I don't have the umbralla. If I have my umbralla with me, you can be sure that it is raining. If I don't have it with me, it mustn't be raining.
If A is a necessary condition of B, that means A must happen for B to happen. In other words, if B happened, A must be true. If A is not true, then B can't happen.
In summary: If B then A. If non A then non B.
Example: I will take my umbralla with me only if it rains.
Raining is a necessary condition for my taking the umbralla with me.
If it is not raining, you can be sure that I don't have my umbralla with me.
Sufficient conditions:
If A is a sufficient condition of B, that means if A happens B must happen. In other words, if B did not happen, A must be false.
In summary: If A then B. If non B then non A.
Example: I will take my umbralla with me if it rains.
Raining is a sufficient condition for me to take the umbralla with me.
If it is not raining, you are not sure whether I have my umbralla with me. But if I don't have my umbralla with me, you can be sure that it is not raining.
Necessary and sufficient
If A is a necessary and sufficient condition for B, that means if A happen B must happen, and if A does not happen, B does not happen. In other words, A=B. It is equivalent with B if and only if A.
In summary: If A then B. If B then A. If non B then non A. If non A then non B.
Example: I will take my umbralla if and only if it rains.
If it is raining, you can be sure I have the umbralla. If it is not raining, I don't have the umbralla. If I have my umbralla with me, you can be sure that it is raining. If I don't have it with me, it mustn't be raining.
Updated on: 02 Mar 2005, 13:38
Originally posted by banerjeea_98 on 02 Mar 2005, 13:18.
Last edited by banerjeea_98 on 02 Mar 2005, 13:38, edited 1 time in total.
Last edited by banerjeea_98 on 02 Mar 2005, 13:38, edited 1 time in total.
Kudos
Bookmarks
Good job....to put this in our heads mathematically, u can deduce these.
----> just like we inverse inequality sign when we multiply -ve, we can perhaps do the same for X---> Y
1) For X--> Y......-ve on both sides will give.....(non Y ----> non X)...note the relation is reversed i.e. Y to X now
2) For (non X ----> Y)......multiply-ve on both sides.....(non Y ----> X)
3) For (X----> non Y).....multiply-ve on both sides.....(Y-----> non X)
Just a thought on mathematical approach for easier recollection.
----> just like we inverse inequality sign when we multiply -ve, we can perhaps do the same for X---> Y
1) For X--> Y......-ve on both sides will give.....(non Y ----> non X)...note the relation is reversed i.e. Y to X now
2) For (non X ----> Y)......multiply-ve on both sides.....(non Y ----> X)
3) For (X----> non Y).....multiply-ve on both sides.....(Y-----> non X)
Just a thought on mathematical approach for easier recollection.
