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Strategy for statistics CR Questions..

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Strategy for statistics CR Questions..

by sachindia » Fri Oct 12, 2012 9:07 pm
The percentage of households with an annual income of more than $40,000 is higher in Merton County than in any other
county. However, the percentage of households with an annual income of $60,000 or more is higher in Sommer County.
If the statements above are true, which of the following must also be true?
(A) The percentage of households with an annual income of $80,000 is higher in Sommer County than in Merton County.
(B) Merton County has the second highest percentage of households with an annual income of $60,000 or more.
(C) Some households in Merton County have an annual income between $40,000 and $60,000.
(D) The number of households with an annual income of more than $40,000 is greater in Merton County than in Sommer
County.
(E) Average annual household income is higher in Sommer County than in Merton County.


Took 2:34 mins to arrive at the right ans. and that was by elimination. Still wasn't 100% sure of the correct ans.
I get stumbled on Questions involving numbers and percentages. Any inputs on strategies to tackles such questions ?

Here's another:
Cheever College offers several online courses via remote computer connection, in addition to traditional classroom-based
courses. A study of student performance at Cheever found that, overall, the average student grade for online courses
matched that for classroom-based courses. In this calculation of the average grade, course withdrawals were weighted as
equivalent to a course failure, and the rate of withdrawal was much lower for students enrolled in classroom-based courses
than for students enrolled in online courses.
If the statements above are true, which of the following must also be true of Cheever College?
(A) Among students who did not withdraw, students enrolled in online courses got higher grades, on average, than
students enrolled in classroom-based courses.
(B) The number of students enrolled per course at the start of the school term is much higher, on average, for the online
courses than for the classroom-based courses.
(C) There are no students who take both an online and a classroom-based course in the same school term.
(D) Among Cheever College students with the best grades, a significant majority take online, rather than classroombased,
courses.
(E) Courses offered online tend to deal with subject matter that is less challenging than that of classroom-based
courses.

took 3.39 mins to arrive at the correct ans. .

On an average how any Questions based on statistics can we expect on the test day?
Regards,
Sach
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by varun289 » Mon Nov 26, 2012 10:27 am
dear my choice will be option A for both questions , my view that u should exact data given in questions , rather focus on trap data
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by David@VeritasPrep » Mon Nov 26, 2012 1:56 pm
Let's deal with your first question first.

First of all there are multiple questions out there with the answer choices rearranged. The Official Answer is the one that in this question is labeled C. In many other problems this same answer choice is rearranged and is B. Regardless of the location that is the correct answer [spoiler](the one that is C in this problem)[/spoiler]

This is an inference question so we can treat as we would any other other inference question which means - process of elimination first! Remember you can eliminate anything that COULD BE FALSE:


A) We can eliminate this - Beyond our knowledge - We do not know that ANY household is over 80,000.

B) We can eliminate this - Beyond our knowledge - We do not know that either of these if "first" or "second" in terms of the $60,0000 category -- the two counties are only compared to each other.

C) You need to keep this one. $40,000 and $60,000 are the important numbers here. We MAY need to come back to look into this one further.

D) You can eliminate this one - Beyond our knowledge - We only know PERCENTAGES, we do not know actual numbers. Merton County may contain the city of London and Sommer County may be in Tibet. Be very careful when working with absolute numbers and percentages at the same time.

E) You can eliminate this one - Beyond our knowledge - We do not know the AVERAGE income of either place. For all we know those who are not making $60,000 in Sommer county are making zero dollars.


So you see - there is no threat here!! The stats do not really matter. You do not even need to prove choice C. You can quickly eliminate the others.

Of course if you think about C - it does have to be true. Let's say that each county has 10 people in it. If Merton County has 5 people with over $40,000 -- Sommer must have fewer (in order to have a lower percentage), so let's say 4 out of 10. Now Sommer has to have a higher percentage over $60,000. So let's say that of those 4 households in Sommer that are over $40,000 all of them are also over $60,000, so 4/10 over $60,000. Now Merton must have a lower percentage over $60,000 so let's say that of those 5 households over $40,000 only 3 of them are over $60,000 so 3/10. You can see that 2 of the households in Merton would have been between $40,000 and $60,0000. In fact, regardless of how the numbers are (I am sure that there are more than 10 households) there must be some households in Merton that fall between $40,000 and $60,000.

Just remember that this last part was not really necessary. 4 of these answers can definitely be eliminated.

Does that help?
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by David@VeritasPrep » Mon Nov 26, 2012 6:28 pm
Now the second question that you posted. How can we deal with this one in less that 3:39?

The second question is is also an Official Guide Question. This question is about Cheever College and is also an inference question. For this type of question you need to focus on the scope of the stimulus -- that is to say exactly what does the stimulus discuss? The majority of incorrect answers on inference questions are those that are outside of what the stimulus actually talks about.

Since there is no "argument" on an inference question in the true sense, but only a set or premises, you can go directly to the answer choices and start to eliminate.

What do we know from the premises? We know that there is a comparison between online courses and traditional classroom courses, we know that the average grades are the same and that more students withdraw from the online courses. The important fact that might make the whole thing is that course withdrawals are equivalent to a course failure.

Let's eliminate choices:

A) seems acceptable --keep it

B) You can eliminate -- the number of students enrolled is beyond our knowledge here.

C) You can eliminate -- I doubt it would matter if any student took both types of classes

D) You can eliminate -- why does it matter if the best students take the courses it is the overall average grade not the top students. And maybe those top students make some bad grades sometimes.

E) You can eliminate -- why does the subject matter make a difference? Students can get good grades in tough subjects.

So you see - again a quick elimination of those four choices. Leaving us with the correct answer (A). We can also prove A with the important fact that I mentioned above..."course withdrawals are treated as equivalent to a course failure" since every withdrawal counts as an "f" and since the online and traditional courses have the same average grade something has to balance the withdrawals, so the online courses must have higher grades from those who do not withdrawal.
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by David@VeritasPrep » Mon Nov 26, 2012 6:33 pm
You asked about statistics on the test and what to expect...

Let me say that the new Veritas Advanced Verbal book deals with the subject of statistics in detail. This is because it is a growing topic on the critical reasoning portion of the GMAT. There is no way to answer your question of "How many CR questions on statistics can we expect on test day?" These questions are just part of the mix like any other CR questions. However, they can be tough so perhaps the better you do the more you will see.

All I can really say is that you should be prepared for stats CR questions because you are prepared for all questions and that is by having strong methods and techniques. As you could see from each of these two questions I was very confident in the elimination of the other 4 choices and I would have been done in about 1 minute or so. That is because I applied good inference question techniques!

A proper approach to statistics questions is a proper approach to critical reasoning questions in general!
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by sachindia » Thu Jan 03, 2013 12:54 am
thanks a lot david
Regards,
Sach
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