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Conclusions from GMAT algorithm study based on ESR analyses

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New post 07 Aug 2016, 03:50
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I somewhat agree with mcelroytutoring here. The first 10 questions are a bit more important than the rest of the questions because they seem to set the difficulty level for the next 15-20 odd questions (but they don't carry any other extra weight). One needs to be extra careful for these questions so that s/he doesn't do silly mistakes on easy to medium difficulty level questions here.

Looking at the ESRs, it is evident that if a person answers a significant no (3-4) of easy/medium questions incorrectly in the first 7 counted non-experimental questions in Quants (or the 8 in verbal), GMAT does not raise the difficulty level much almost for the rest of the exam. Now, I believe, this is more because these people continue to do a few mistakes here and there for the following medium difficulty questions. My hypothesis is that if you do answer the next 15-20 questions all correctly, it will raise the difficulty level again and you can still get a high score if you can answer the difficult questions correctly in the last part. However, I admit that I have not seen such an ESR, probably because if a person is doing 3-4 mistakes in the first 7-8 easy to medium questions, then it is not possible for him / her to answer 15-20 questions on the traught with 0-1 mistake.

So, to avoid silly mistakes in the first 10, one needs to spend more time there. Now, the question is how much more is justified? In my opinion, about 15% more than average time should be good enough to re-check the answers for silly mistakes as a good student should know from his practice experience where s/he is prone to silly mistakes and should check those areas. Now, if you are not sure where you are doing your silly mistakes then that's a different question and spending some extra time in the first few questions will not help.

For example, in Quants one has about 2 minutes on average per question. So the first 10 should take about 20 minutes. A 15% grace will give you 23 minutes for the first 10 questions. That's in my opinion optimum and one should not cross that time limit. Otherwise, s/he might run into a severe timing issue.

However, I agree with others that if you are generally good and looking for high score then you should be more concerned about answering more difficult questions throughout the exam rather than concentrating too much on the first few questions.
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Last edited by himpuju on 08 Aug 2016, 04:35, edited 1 time in total.

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Re: Conclusions from GMAT algorithm study based on ESR analyses [#permalink]

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New post 07 Aug 2016, 04:21
I can imagine "experimental" questions in Quant such as a problem that probably is hybrid in nature or something that does not require application of usual math. However, how do experimental questions in verbal look like? verbal has a very definite curricula when compared with the Quant. Any idea?

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New post 07 Aug 2016, 11:46
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Senthil7 wrote:
I can imagine "experimental" questions in Quant such as a problem that probably is hybrid in nature or something that does not require application of usual math. However, how do experimental questions in verbal look like? verbal has a very definite curricula when compared with the Quant. Any idea?


Senthil, the experimental questions are like any other normal non-experimental GMAT questions. You cannot differentiate them in any way. According to GMAT experts, they are there to gauge the difficulty level of the questions as after they are used for a certain large no of GMAT test-takers, GMAC will know what percentage of test-taker get it right. They then set the difficulty accordingly and use the question as a non-experimental or scored one in GMAT. Please see the below discussion -

http://gmatclub.com/forum/dummy-questions-on-gmat-220747.html

You can probably guess whether a question is an experimental one if the difficulty level is understandably different from the questions around it i.e. you get a very easy question in between two difficult question or you get a very difficult question in between two easy questions. However, it will still be a guess and you can never be sure as your perception of difficulty in a topic might be different from other test-takers. So, it is best that you don't think about experimental questions at all and answer every question to the best of your ability. However, if a question is too difficult for you then you can always guess it, move on and hope that it was an experimental question.. :)
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New post 07 Aug 2016, 13:02
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mvictor wrote:
HanoiGMATtutor wrote:
mvictor wrote:
strange thing though with verbal
V38
first part 62%
second part 57%
third part 71%
fourth part 62%

mine 30:
1st - 62%
2nd - 71%
3rd - 86%
4th - 62%

although I was better of overall, I got a lower score.
I really don't understand why getting to the hard verbal questions is so hard, even though you answer questions correctly...


It could be the case that the V38 started out stronger and was put on a higher bracket and therefore faced more difficult questions, resulting in a lower accuracy ratio but a higher score. We'll know for sure if the poster shares the average difficulty chart.


but if the difficulty level started at a higher than medium level, it automatically makes the test unfair!!!
hope we'll see the difficulty level chart..
it might be the case that he got no experimental questions in the first set, while I got lots of them, which in the end did not count towards the final score and difficulty level overall..


This is the problem with splitting up the ESRs into quarters...question #12 matters a lot more than does question #20, but they are in the same quarter of questions. It's also important to remember that each collection of GMAT questions may be scored on a slightly different curve, which we have seen evidence of in the IR section.

In other words, you may have struggled at the beginning of the 2nd section, thus "earning" an easier question difficulty level and making your score drop more, despite the fact that you recovered quickly and actually performed better overall. The problem is that you may have performed better overall, but on easier questions.
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New post 09 Aug 2016, 06:48
himpuju wrote:
Looking at the ESRs, it is evident that if a person answers a significant no (3-4) of easy/medium questions incorrectly in the first 7 counted non-experimental questions in Quants (or the 8 in verbal), GMAT does not raise the difficulty level much almost for the rest of the exam. Now, I believe, this is more because these people continue to do a few mistakes here and there for the following medium difficulty questions. My hypothesis is that if you do answer the next 15-20 questions all correctly, it will raise the difficulty level again and you can still get a high score if you can answer the difficult questions correctly in the last part.


I have found one verbal ESR (see below) which actually supports my hypothesis above. If you check the verbal ESR below, you can see the person did not start the test well. He got 3 out of 8 incorrect in the first quarter and 3 out of 7 incorrect in the second quarter. As a result, he got only about medium level questions in the 3rd quarter on an average. But here he answered all questions correctly and GMAT raised the difficulty in the last quarter, where again he answered every counted question correctly and ultimately scored a V40 which is a very good score. His accuracy in the first half was 60%, but an accuracy of 100% in the second half helped him recover. Please note, he still did not miss any easy question in the first half, he only answered medium to difficult questions incorrectly there.

Attachment:
GMATVerbal_40.jpg
GMATVerbal_40.jpg [ 109.93 KiB | Viewed 1313 times ]


Now, he answered 24 out of 30 counted questions correctly and got a V40. I will compare this to my own verbal ESR (see below) as I also answered 24 out of 30 counted questions correctly and got a V41. The difference was that I was more consistent in the four quarters (around the 80% mark). Due to this, the average difficulty of the questions given to me in the 2nd and 3rd quarter was slightly higher than the ones given to him in the respective quarters. He recovered remarkably in the last quarter and answered questions of more average difficulty than me as I did some mistakes there and the average difficulty of the questions given to me remained the same. So, I got 2 quarters with more difficulty and he only got one quarter. So, the opportunity to answer more questions with a slightly higher difficulty level helped me with 1 point, even though the total no of correct question was same.

Attachment:
himpuju.jpg
himpuju.jpg [ 147.95 KiB | Viewed 1311 times ]


Now, you might ask that’s only 1 point and there might not have been any improvement in the overall score due to this. So, what’s the fuss about this? Have a look at the timing of the quarters and you will be surprised. This person have taken way less time than the average in quarter 1, 2 and 4. He actually finished the verbal section 20 minutes to spare. It is evident from his performance in the second half that he has a strong grasp over GMAT verbal and can answer difficult questions correctly and consistently in less than the average time. Had he taken some time in the beginning to be extra careful as he did in quarter 3, he would have probably got at least a V44 or V45. That would have been a 20-30 points jump. Most people will not be able to emulate this second half performance in the actual exam due to time pressure and fatigue unless they are as strong in verbal as this person is. So, most people will end up with a lower score if they have a start like that.

However, I would caution everyone not to spend too much time in the first quarter so that they are under time pressure in the later parts. You should have a definite timing strategy and practice that with GMATPrep tests. Don’t change your timing strategy in the actual GMAT. Use the timing strategy that you employed in the GMATPrep. Yes, during the last few questions the difficulty level is set for you. But you still need to answer them correctly. Otherwise your score may take a dip. Check the ESR below. The person maintained 86% accuracy for the first 3 quarters and was on course for a 40+ in verbal. However, only 38% accuracy in the last quarter hurt and the person could score 38, which is still very good, but he would have surely got 40+ if he could have had a 62% accuracy in the last quarter. He was under no time pressure for that. This supports that you still have to maintain your accuracy through the last quarter if you are targeting a high score. The last few question do carry the same weight as claimed by GMAC.

Attachment:
Verbal_38_3.jpg
Verbal_38_3.jpg [ 130.26 KiB | Viewed 1311 times ]

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New post 09 Aug 2016, 10:40
I just gave the gmat prep exam today... i saw it was written in one of the posts above that the gmat prep is different from the actual gmat.. not sure what that meant... but anyway.. i got a q50.. what struck me was that i got that despite getting all of the last 3 of the questions wrong ... my other 6 wrong questions being.. Number 4 .. 14 .. 16... 20...29..30.. (35 to 37 being the last three)..

Atleast on the gmatprep the first twn are imp. Is wat i could infer..

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New post 09 Aug 2016, 11:16
KSHITIJ205 wrote:
I just gave the gmat prep exam today... i saw it was written in one of the posts above that the gmat prep is different from the actual gmat.. not sure what that meant... but anyway.. i got a q50.. what struck me was that i got that despite getting all of the last 3 of the questions wrong ... my other 6 wrong questions being.. Number 4 .. 14 .. 16... 20...29..30.. (35 to 37 being the last three)..

Atleast on the gmatprep the first twn are imp. Is wat i could infer..

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First of all congrats for your q50. How can you say exactly what questions are wrong ? It's clear that you guessed the last 3 questions. Anyway you may got your experimental questions wrong ( other 6).


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New post 09 Aug 2016, 11:19
chaitanya87 wrote:
KSHITIJ205 wrote:
I just gave the gmat prep exam today... i saw it was written in one of the posts above that the gmat prep is different from the actual gmat.. not sure what that meant... but anyway.. i got a q50.. what struck me was that i got that despite getting all of the last 3 of the questions wrong ... my other 6 wrong questions being.. Number 4 .. 14 .. 16... 20...29..30.. (35 to 37 being the last three)..

Atleast on the gmatprep the first twn are imp. Is wat i could infer..

Posted from my mobile device

First of all congrats for your q50. How can you say exactly what questions are wrong ? It's clear that you guessed the last 3 questions. Anyway you may got your experimental questions wrong ( other 6).


Sent from my iPad using Tapatalk


He is talking about GMATPREP mock and not an actual GMAT. This is the reason why he knows where or on what questions did he made a mistake.
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New post 11 Aug 2016, 08:43
mcelroytutoring wrote:

HKD1710 (Q45) - 57 57 71 100

mvictor (Q49) --- 71 57 71 100

Finally, someone who agrees with me... : ) hiline-gmat-algorithm-studies-223122.html#p1718357

I would also like to point out that those numbers represent a difference of only one correct question in the 1st quarter, yet they resulted in a 4-point score differential! Despite what the GMAC and others might try to tell you, the "myth" of the outsized importance of the first 9-10 questions is anything but.

4/7 counted questions in the 1st quarter = 57%

5/7 counted questions in the 2nd quarter = 71%


So do you think this 1 question spoiled my score completely? 1 questions = 4 point drop! isn't that huge??
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New post 11 Aug 2016, 09:02
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HKD1710 wrote:
mcelroytutoring wrote:

HKD1710 (Q45) - 57 57 71 100

mvictor (Q49) --- 71 57 71 100

Finally, someone who agrees with me... : ) hiline-gmat-algorithm-studies-223122.html#p1718357

I would also like to point out that those numbers represent a difference of only one correct question in the 1st quarter, yet they resulted in a 4-point score differential! Despite what the GMAC and others might try to tell you, the "myth" of the outsized importance of the first 9-10 questions is anything but.

4/7 counted questions in the 1st quarter = 57%

5/7 counted questions in the 2nd quarter = 71%


So do you think this 1 question spoiled my score completely? 1 questions = 4 point drop! isn't that huge??


Yes, the score differential was mostly a function of that 1 question in the first quarter, which, given the ESR data, seems to determine some sort of cutoff line between earning mostly medium vs. mostly hard questions during the remainder of the test.

The other student was rewarded for performing equally well on the final 3 quarters, despite receiving generally harder questions, due to his/her slightly better performance (yes, only a 1-question difference!) in the first quarter. There is no way for sure to say that you would have done the same. Still, 4 points for 1 question is pretty nuts.
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New post 11 Aug 2016, 10:50
HKD1710 wrote:
So do you think this 1 question spoiled my score completely? 1 questions = 4 point drop! isn't that huge??


I think the 1 questions = 4 point drop is a bit oversimplified equation here. You need to consider the difficulty level as well. He answered the same no of questions correctly in the last 3 quarters but most of those questions were of higher difficulty. That is why he is rewarded with 4 point more. He not only performed better in the first part as he got one more question correct, but also performed better in second and third part as he only missed 3 hard questions in the second and 2 hard questions in the third. Whereas you missed 3 medium questions in the second and 2 moderately hard questions in the third. GMAT did not raise the difficulty level much as you continued to miss medium questions in the second quarter. The key thing is not to answer too many medium or easy questions incorrectly in the first two quarters.

The only way for you to recover in the second quarter was to answer all medium level questions correctly so that you could force the GMAT to raise the difficulty level to hard. But it never happened, so you never got so called hard questions.

Also, another probability is that the 3 questions that you missed in the second quarter were medium level questions near the start of the quarter, whereas the 3 questions missed by mvictor might have been the hard questions around the end of the quarter. Please note, GMAT adjusts the difficulty level gradually considering all the counted question answers before that. However, the ESR only shows the average of 9-10 questions. A lot may depend what has happened in the beginning of a quarter or in the end of the quarter.
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Re: Conclusions from GMAT algorithm study based on ESR analyses [#permalink]

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New post 13 Aug 2016, 05:56
mcelroytutoring wrote:
HiLine wrote:
The ESR's that you have posted do not support that conclusion.

What you are doing is comparing two scenarios that are not equivalent.

A candidate who answers 3 questions wrong at the beginning and answers the rest of the questions correctly is going to score less than one that answers 3 questions wrong at the end and answers the rest of the questions correctly, because the latter tackles more challenging questions at the same level of accuracy and thus should be deemed a more competent candidate.


What I am hearing from most of you who disagree with me is that "test-takers who do well on the first quarter of questions are better GMAT students who earn harder questions, and thus deserve better GMAT scores". Overall, of course this is true, but it does not change my point about the unfairly "front-loaded" nature of how GMAT scores are determined.

My point is that 9 questions is not large enough of a sample size to fully determine someone's "initial" GMAT skill level, and hence there is an element of luck involved in scoring well. Answer fewer than 5 out of the first 7 counted questions correctly, and your chances for an elite score are almost zero. Throw in the fact that 2 of those first 9 questions are experimental and don't count toward your score, and this adds even more randomness into the equation. You could answer 7 out of 9 correctly, and the 2 you got wrong were experimental (100% correct), or you could get 7 out of the 9 right, but 2 of the correct answers could have been experimental (5/7 = 71%). This is of course not only true about the first quarter of the test, but the entire GMAT, where nearly 25% of the questions are experimental.

Yes, it is true that correct responses (normally--see below) earn harder questions, and consistently answering medium/hard questions correctly is the best path to a great GMAT score. But the student won't even get the chance to try hard questions if the GMAT algorithm makes early, "snap" judgements about his/her skill level, which it does. Anyone who is out there reading this: don't take my word for it--take a look at the ESRs and decide for yourself! The evidence is readily available if you're willing to take a look: information-on-new-gmat-esr-report-beta-221111.html

Any statistician knows that in order to provide an accurate measurement across a large population, you need a large sample size. A score estimate based on a small sample size of GMAT questions is more prone to fluctuations based on lucky / unlucky guesses and other random elements. But perhaps this is exactly what the GMAC wants, so that you will keep paying $250 to take the GMAT again and again.

Also, the first questions are not easy difficulty--they are medium difficulty.

What's interesting about the first 10 questions "myth" is that the GMAC does not directly dispute it...instead it just uses vague, roundabout language such as "all questions count." Yes, all questions count, but that doesn't mean that earlier questions don't affect your score more strongly than do later questions, because in fact they do, and the data from the ESRs supports this.

The excerpt below is taken directly from the OG 2016:

"Myth -vs- FACT–
M
- The first 10 questions are critical and you should invest the most time on those.
F – All questions count. It is true that the computer-adaptive testing algorithm uses the first 10 questions to obtain an initial estimate of your ability; however, that is only an initial estimate. As you continue to answer questions, the algorithm self-corrects by computing an updated estimate on the basis of all the questions you have answered, and then administers items that are closely matched to this new estimate of your ability. Your final score is based on all your responses and considers the difficulty of all the questions you answered. Taking additional time on the first 10 questions will not game the system and can hurt your ability to finish the test."


Like the rest of the GMAT, this text requires a close reading. Notice that not even the GMAC disputes that the first 10 questions have a larger impact on your final score than does any other group of 10 questions. Yes, spending too much time on the first 10 can hurt your score if you don't do so correctly (you need to save time for the remaining 27 questions, of course), but this does not change the fact that doing well on those first 10 questions is essentially mandatory for a top GMAT score. GMAT calls it an "initial estimate," but this is simply a euphemism for a snap judgment. Yes, adjustments to one's score continue to be made throughout the test, but the "Average Difficulty" charts on the ESRs support the notion that the largest adjustments in difficulty/scoring occur early in the test, and a close reading indicates that the GMAC does nothing to directly dispute this notion (although it tries its best to imply that this is untrue).

For example, the below performance of (broken down by quarters) 100% / 100% / 57% / 29% on Quant earned a 47 out of 51 (also mentioned in my original post). Not bad for getting more than half of the final 14 counted questions wrong.

Image

To some perfectionistic students, a score of Q47 would be a disappointment. But to many others, it would be a dream come true. This ESR shows that you can essentially turn the GMAT Quant into a 25-question test, take aggressive guesses on the final 12, and still achieve an above-average Quant score.

Should you "invest the most time" on the first 10 questions? Of course not--that's barely 25% of the questions. The GMAC is setting up its own straw man here, to avoid addressing the real issue at hand. You should not spend most of your time on the first 10 questions, but you should spend more time per question on those questions than you do on the remaining ones, given their outsized importance to the scoring algorithm.

Also, you mentioned in your original post (heading #3) that the difficulty level seemed to drop, despite the student answering questions correctly, and that you weren't sure why.

HiLine wrote:
This is the conclusion that puzzled me the most:

Sometimes, when you're doing too well, e.g. answering all questions correctly, the difficulty of questions drops.


I think that this passage (also from the OG 2016) should clarify the issue for you:

"Myth -vs- FACT-
M
– Getting an easier question means I answered the last one wrong.
F – Getting an easier question does not necessarily mean you got the previous question wrong. To ensure that everyone receives the same content, the test selects a specific number of questions of each type. The test may call for your next question to be a relatively difficult problem-solving item involving arithmetic operations. But, if there are no more relatively difficult problem-solving items involving arithmetic, you might be given an easier item. Most people are not skilled at estimating item difficulty, so don’t worry when taking the test or waste valuable time trying to determine the difficulty of the questions you are answering."


Hi,

Did the student overcome 47 at the end? I have almost exactly the same picture:) except that I got 57% and 43% correct in the last 2 quarters

Sorry for off-topic

Best regards,
Dauren

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New post 09 Oct 2016, 20:17
I have updated post #2 with compilations of number of questions wrong vs sectional score.

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Senthil7 wrote:
So now we are being driven to conclude that no part of the exam must be given undue importance or be neglected, rather focus on every question! This is contrary to what I have read on top prep companies websites and many topics in here. So skipping questions (as promoted by certain prep companies and many individuals) is just a sign of moving over inability and nothing tactical as no one knows which questions is experimental.
.
In such a case, would a sound advise be to work on every question and not simply guess and move on?


Guessing on GMAT questions before you have fully figured them out ("punting") is a calculated risk. If you don't understand a question, then all the time in the world might not help, so at a certain point you need to cut your losses, move on to the remainder of the questions in the section, and hope that the question you guessed on was an experimental ("pretest") question.

However, I would give earlier questions about 15-20% more time than later questions before giving up, given their outsized importance to your score.
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There’s one finding that I can’t really figure out the reason for it. For the person 1, he scored a 780 total with verbal 48. He was offered the questions in Verbal section with difficulty levels: Medium-Medium High-Medium-Medium High in the four quarters respectively. I think we can agree with the level of difficulty questions that were offered to him.
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However for the person 2, even he was offered with the same set of difficulty questions (Medium-Medium High-Medium-Medium High).
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So what is the basis for choosing this pattern of difficulty level for the two persons?? I suppose we all can agree that in the final quarter most of us are racing against time and mostly have to guess a few of the remaining questions, so in that case guessing on the Medium High level question will anytime give us more credits as opposed to guessing on the Medium level questions, no???

PS: I have taken both of these snapshots from the ESRs posted in the forum: Information on NEW GMAT ESR REPORT - BETA - Upload yours here

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Question for mcelroytutoring or others: In view of these observations, what would you recommend to someone who is shooting for initial 45Q? Is it a better use of time to focus on medium-level questions across multiple GMAC packages, (difficulty determined by GMAC's OG Wiley interface for example), to make sure to get into mid 40s, before practicing difficult questions? I am afraid of not getting into hard question "territory" at all on the exam and wasting time on practicing questions I will never be given. Any info is much appreciated.

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HiLine wrote:

5. Impact of number of questions wrong on scores



These are the rough ranges for the number of questions people have got wrong to achieve a certain score:

Q51: 0-2
Q50: 2-4
Q49: 4-8
Q48: 6-9
Q47: 7-11
Q46: 10
Q45: 10-11

Keep in mind that these are out of the 30 Quant questions that count

V48: 1
V47: 2
V46: 3
V44: 3-5
V42: 4
V41: 4-6
V40: 7
V38: 8-11
V37: 8-9
V36: 9-10
V35: 9-12
V34: 7-11

Keep in mind that these are out of the 28 Verbal questions that count


This list has been slightly updated. It is pretty much on point ;)

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New post 30 Aug 2017, 00:21
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HiLine wrote:
HiLine wrote:

5. Impact of number of questions wrong on scores



These are the rough ranges for the number of questions people have got wrong to achieve a certain score:

Q51: 0-2
Q50: 2-4
Q49: 4-8
Q48: 6-9
Q47: 7-11
Q46: 10
Q45: 10-11

Keep in mind that these are out of the 30 Quant questions that count

V48: 1
V47: 2
V46: 3
V44: 3-5
V42: 4
V41: 4-6
V40: 7
V38: 8-11
V37: 8-9
V36: 9-10
V35: 9-12
V34: 7-11

Keep in mind that these are out of the 28 Verbal questions that count


This list has been slightly updated. It is pretty much on point ;)


These numbers are helpful guidelines--thanks! However, today I took the GMAT and scored a Q50, despite getting 6 questions wrong out of the 30 counted questions--I think that these "questions wrong" ranges might be a lot wider than they appear, since we know that on the GMAT, *where* you get the questions wrong matters almost as much, if not more, than *how many* questions you you get wrong.

I also scored a V42 with 5 questions wrong out of the 28 counted questions.

My debrief and ESR: https://gmatclub.com/forum/gmat-tutor-debrief-finally-cracked-q50-q50-v42-ir8-750-composite-248190.html#p1916781
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New post 31 Aug 2017, 18:10
The more data points the better. Thanks for your contribution, mcelroytutoring!

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New post 17 Oct 2017, 02:46
Amazing post the fact and suggestions were given are the ground reality and was quite apt for this very exam. thanks for this kind

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