The name of the technique is assumption negation technique (ANT). It is used for assumption questions only. The logic of using the technique is this:

An assumption is a necessary missing premise. It is NECESSARY for the conclusion to hold. If the assumption is negated, the conclusion cannot hold. Hence, it is a check to see whether a statement is actually an assumption or not.

Check out how to use the ANT here:

http://www.veritasprep.com/blog/2013/03 ... -the-gmat/
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what is the best approach to solve problems like these.
I always find multiple options correct in these kind of questions and it is very diffucult to select correct one within 2 mins.
Anybody can put down a sound approach to tackle problems like these ??
Thanks in advance.

In must be true questions, if you are not sure whether the statement must hold, try to find a case where it may not hold.
Try to make it false within the scope of the information given in the argument.

Argument:
Everyone who graduates from topnotch high school has IQ > 120.
Most > 120 and all > 150 students who apply get accepted to at least one Ivy league university.

For example, in option (B) above,

B]If a person is a high-school graduate and has an IQ of less than 100, he or she could not have been a student at TopNotch High School.

Now try to make this false. Can we have a high school graduate with IQ 100 who could have been a student at TopNotch? The important point here is "could have been". Sure. Perhaps she graduated from another school but could have been a student here before that. So it needn't be true - it could be false. She could have been a student at TopNOtch. So this is not the answer.
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Hi EMPOWERgmatRichC

Could you please provide your comments on this.

I want to know what is the issue with option B?


Regards

The argument states that everyone who has graduated from Top Notch High school has an IQ over 120. "B" states that if a person is a high school graduate and has an IQ of 100, he or she could not have been a student at Top Notch High school. The case might be that this student studied in Top Notch High school for a while and the then shifted to some other school from where he graduated. In that case the conclusion does not hold. Hence "B" cannot be a possible answer
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Hi PathFinder007,

This is an Inference question. To be 100% clear on our assignment with this question, we have to be able to look at the correct option and say, "yup, I know that for an absolute fact."

Let's pull up the salient points:
Everyone who has graduated from TopNotch High School has an intelligence quotient (IQ) of over 120. Most students with an IQ of over 120 and all students with an IQ of over 150 who apply to one or more Ivy League universities are accepted to at least one of them.

The statements above, if true, best support which of the following conclusions?

B) If a person is a high-school graduate and has an IQ of less than 100, he or she could not have been a student at TopNotch High School.

Is it possible that TopNotch could have had STUDENTS (not graduates) with IQs of less than 100? Yes. From the information we're given, we can't rule out that possibility. For all we know, TopNotch could have had a student with a 99 IQ who got booted from the program and never graduated. That means we have to get rid of option B.

Bigger Picture: There's a reason why this question is rated at a 95% difficulty quotient. The granularity of these options, particularly B, reaches an unusual level.
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I am trying to understand why D) is incorrect.
We know that "Most students with an IQ of over 120 who apply to one or more Ivy League universities are accepted to at least one of them"
say 10 students from TopNotch high school (120<IQ<150) applied to one or more IVY league Universities, since most of them are accepted to at least one of them, we can expect at least 6(i.e. most of them) get accepted to one of the IVY leagues.
I see that C is a clear answer. But I am not able understand why D is wrong.

Here is why:

Argument:
Everyone who graduates from topnotch high school has IQ > 120.
Most > 120 IQ and all > 150 IQ students who apply get accepted to at least one Ivy league university.


4]At least one graduate from TopNotch high school who has applied to at least one Ivy-League university has been accepted to one of them.
Not necessary. It is possible that no student from top notch has IQ > 150 or even if there are students with IQ > 150, they may not have applied. We know that most students with IQ > 120 who apply get accepted but it is possible that all those who applied from top notch (and hence had IQ>120) got rejected. (Number of people who applied from top notch could be a very small % of the total number of people with IQ > 120 who applied)

Say this year 1000 students with IQ greater than 120 applied to Ivy League universities. Say only 20 of them did not get accepted to any university so most got accepted.
It is possible that all students of Top Notch who applied fall in this 20. What if only 5 of Top Notch had applied and all 5 are in this 20? Then (D) is not true.
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Reading the passage, we have below info:

• All TopNotch graduates has IQ > 120
• Most students of IQ>120 who apply to >=1 Ivy League schools get accepted to by >=1
• All students of IQ > 150 who apply to >=1 Ivy League schools get accepted by >=1

Note the condition comes with 'who apply to", while this answer failed to include that piece of info, incorrect


Be careful with the shell game here: the first part of sentence use "graduate" while the 2nd part uses "student". It could be a student who studied at TopNotch but got transferred to another high school and graduated with IQ < 100, incorrect


"It is possible" signals this might be a good contender, and it suffices "all TopNotch graduates has IQ >120". Correct answer


Note we have a gap in given condition "Most students of IQ>120 who apply to >=1 Ivy League schools get accepted to by >=1". Let's say 80% of the students with IQ >120 and actually applied got accepted, there is still a chance (even though very low) that all TopNotch graduates fill in the rest 20% who failed.


Shell game again: the answer said "not attending" while all given conditions emphasize "acceptance". The graduate could have been accepted but choose not to attend for whatever reason.

I just can't understand one thing:

I can infeer that, if a person have a 150 IQ, it's not sure that this person will be accepted?

In my mind, there is a difference between "over 150" and 150+.

Over 150 => x>150
150+ => x is greater or equal than 150.

It is correct to think that way to exclude A and E?