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Necessary and sufficeint Questions

Author Message
Director
Status: Final Lap Up!!!
Affiliations: NYK Line
Joined: 21 Sep 2012
Posts: 934
Location: India
GMAT 1: 410 Q35 V11
GMAT 2: 530 Q44 V20
GMAT 3: 630 Q45 V31
GPA: 3.84
WE: Engineering (Transportation)

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29 Dec 2012, 16:29
1
Hello all

I am initiating this discussion to clear my doubt on Necessary and Sufficient questions.

Sufficient condition : This is the part of conditional statement that indicates the occurance of necessary condition.
Necessary Condition : This condition is a part of the condition statement the occurance of it is required for the sufficient condition.
Typical example:-

If you get an A+, then you must have studied

Sufficient Condition : Get an A+
Necessary condition: You must have studied.

Another example
People who drive fast are dangerous

Sufficient condition: Drive fast
Necessary condition: Dangerous

My doubt is should we consider parallel thinking in such question i.e. Should we think that A dangerous person can have several traits and driving fast is one of them.
Or When we are considering Necessary and Sufficient condition we must stick to the fact that there exists only one condition as stated in the statement.
Is it correct to say " People who are dangerous, its not necessary that they drive fast"
Justification: There may be many people who are veteran criminal but while driving drive slowly because they do not want accident.

My Query is Should we restrict ourselves to the two conditions itself when answering such question or think logically as we do on all other CR questions. If we follow the logical procedure then the the mentioned statement with justification should be correct. But if we just restrict ourselves to two events than we can write it as " People who are not dangerous, they do not drive fast" i.e People whoare dangerous must drive fast...Its illogical in real world.

PLs help me to clear my doubts.
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 8787
Location: Pune, India
Re: Necessary and sufficeint Questions  [#permalink]

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29 Dec 2012, 18:40
1
1
Archit143 wrote:
Hello all

I am initiating this discussion to clear my doubt on Necessary and Sufficient questions.

Sufficient condition : This is the part of conditional statement that indicates the occurance of necessary condition.
Necessary Condition : This condition is a part of the condition statement the occurance of it is required for the sufficient condition.
Typical example:-

If you get an A+, then you must have studied

Sufficient Condition : Get an A+
Necessary condition: You must have studied.

Another example
People who drive fast are dangerous

Sufficient condition: Drive fast
Necessary condition: Dangerous

My doubt is should we consider parallel thinking in such question i.e. Should we think that A dangerous person can have several traits and driving fast is one of them.
Or When we are considering Necessary and Sufficient condition we must stick to the fact that there exists only one condition as stated in the statement.
Is it correct to say " People who are dangerous, its not necessary that they drive fast"
Justification: There may be many people who are veteran criminal but while driving drive slowly because they do not want accident.

My Query is Should we restrict ourselves to the two conditions itself when answering such question or think logically as we do on all other CR questions. If we follow the logical procedure then the the mentioned statement with justification should be correct. But if we just restrict ourselves to two events than we can write it as " People who are not dangerous, they do not drive fast" i.e People whoare dangerous must drive fast...Its illogical in real world.

PLs help me to clear my doubts.

We discuss necessary and sufficient conditions in detail in our book. It is an extremely important concept. There is a diagram that looks like this:

Necessary 1 ----->
Necessary 2------>
Necessary 3------> Sufficient Condition
...

All necessary conditions together lead to the sufficient condition. If the sufficient condition takes place, it means all necessary conditions took place. If one necessary condition takes place, we dont know whether the sufficient condition took place or not since we dont know whether the other necessary conditions took place. If even one necessary condition did not take place we can easily say that the sufficient condition did not take place.

People who drive fast are dangerous

Sufficient condition: Drive fast
Necessary condition: Dangerous

This means you need to be dangerous to be able to drive fast. To 'drive fast', there are various necessary conditions. 'Being dangerous' is one of them.

Quote: "Should we think that A dangerous person can have several traits and driving fast is one of them."
No, you should think that people who drive fast have several traits. Being dangerous is one of them. The sufficient conditions could need many necessary conditions. Not the other way around.

Quote: "Is it correct to say " People who are dangerous, its not necessary that they drive fast"

Yes it is. Being dangerous is a necessary condition. We don't know whether it alone leads to the sufficient condition of driving fast.

Check out my recent posts on my blog (link is in my signature). They tackle necessary and sufficient conditions.
_________________

Karishma
Veritas Prep GMAT Instructor

Director
Status: Final Lap Up!!!
Affiliations: NYK Line
Joined: 21 Sep 2012
Posts: 934
Location: India
GMAT 1: 410 Q35 V11
GMAT 2: 530 Q44 V20
GMAT 3: 630 Q45 V31
GPA: 3.84
WE: Engineering (Transportation)
Re: Necessary and sufficeint Questions  [#permalink]

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29 Dec 2012, 18:49
HI Karishma
That means
If just necessary condition is mentioned for an action to be sufficient we should not assume that there are many others, If it is not explicitly mentioned in the argument.
Necessary1--> Sufficient
There may be many other but we ar oncerned her only about necessary 1
Necessary1, Necessary2, Necessary3------------> Sufficient
All 3 are needed for the condition to be sufficient.Other than these we are not concerned about any....

regards
Archit
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 8787
Location: Pune, India
Re: Necessary and sufficeint Questions  [#permalink]

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29 Dec 2012, 19:01
Archit143 wrote:
HI Karishma
That means
If just necessary condition is mentioned for an action to be sufficient we should not assume that there are many others, If it is not explicitly mentioned in the argument.
Necessary1--> Sufficient
There may be many other but we ar oncerned her only about necessary 1
Necessary1, Necessary2, Necessary3------------> Sufficient
All 3 are needed for the condition to be sufficient.Other than these we are not concerned about any....

regards
Archit

If a necessary condition is mentioned for a sufficient condition, we know that there is at least this condition necessary. There could be others too, we should not forget that. This necessary condition alone may not be enough to make the sufficient condition take place.

Remember:
Necessary1, Necessary2, Necessary3------------> Sufficient

All 3 are required to make the sufficient happen.

But if the sufficient happens, we know all three necessary conditions took place.
_________________

Karishma
Veritas Prep GMAT Instructor

Intern
Joined: 16 Oct 2015
Posts: 8
Re: Necessary and sufficeint Questions  [#permalink]

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08 May 2016, 01:54
HI,
How to differentiate between sufficient and necessary questions ? Are there any keywords that differentiate the two ?
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 8787
Location: Pune, India
Re: Necessary and sufficeint Questions  [#permalink]

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08 May 2016, 21:45
1
3
SecondTymRockStar wrote:
HI,
How to differentiate between sufficient and necessary questions ? Are there any keywords that differentiate the two ?

http://www.veritasprep.com/blog/2012/11 ... tatements/
http://www.veritasprep.com/blog/2012/12 ... tatements/
http://www.veritasprep.com/blog/2012/12 ... onditions/
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Karishma
Veritas Prep GMAT Instructor

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Joined: 01 Oct 2013
Posts: 3593
Re: Necessary and sufficeint Questions  [#permalink]

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09 Jun 2018, 03:29
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Re: Necessary and sufficeint Questions &nbs [#permalink] 09 Jun 2018, 03:29
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