ankurjohar wrote:

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 classroom- based,

courses.

(E) Courses offered online tend to deal with subject matter that is less challenging than that of classroom-based courses.

I am facing difficulty in solving this problem.

Using Inference technique as mentioned, i was able to eliminate

Option C - OFS

Option D - OFS (best grade is not talked in the passage)

Option E - OFS (less complex subject not discussed in argument)

Option A - iSAWT (I felt student who didnt withdraw got higher score is not right answer choice as the argument is only about the enrolled/withdrawl student count)

Hence, I marked option B as right choice.

Please help me in understanding what i am missing in making logical structure of this argument and in doing pre-thinking.

Thanks,

Ankur

Hi Ankur,

You are correct in rejecting options C, D, and E as OFS.

However, the reasons for selecting option B and rejecting option A are correct.

First, let's talk about option B:

(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.

Nowhere does the passage talk about number of students. The passage only talks about withdrawal rate, which refers to proportion of students who withdraw from the course. We do not know anything about the number of students in either traditional or online courses. So, option B is incorrect.

Coming to option A:

(A) Among students who did not withdraw, students enrolled in online courses got higher grades, on average, than students enrolled in classroom-based courses.

You are correct that the passage only talks about students who withdrew and not about students who did not withdrew. But what is the relation between students who withdrew and students who did not withdrew?

The relation is:

Students who did not withdrew + Students who withdrew = Total number of students enrolled

Now, we are given average grade for all the enrolled students and we also know average grade of Students who withdrew - the grade is "0" or "failed". From this, don't you think we can make some judgement about the average of students who did not withdrew.

We can!

If average grade for "all enrolled students" was same for traditional and online courses

And "Number of students who withdrew i.e. who got "Fail" grade" were higher for online courses than traditional courses

Then, in such a case, the average grade of students who did not withdrew must be higher for online courses than traditional courses.

Do you get it?

If you look back now, you can see that Students who did not withdrew and Students who withdrew constitute all the students. Right?

In such cases, where two sets constitute everything or the universe, then in a lot of cases, on the basis of information of one set, we can make inferences about the other set.

Does it help?

Thanks,

Chiranjeev

_________________

Aiming to score 760+ on the GMAT? Attend our free webinar to learn how to define your GMAT strategy, create your study plan and master the core skills to excel on the GMAT. Click here to register for this webinar. The webinar will start at 7 AM PST on the 6th of June 2015.