Critical Reasoning

From OG12.Could someone explain the reasoning please?

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.

IMO: E

A

More people withdraw from online courses , at the same time the average grades for both courses are same.So classroom courses must have higher gradings, on average.

+1 for A

Why is B wrong?

GmatKiss wrote:IMO: E

You can not assume that the more challanging a lesson, the more people fail!
This is very common trick for GMAT!. Be aware!
You have to follow premises and stay within the argumentT

@singalong:
If you can justift your answer , then you can be convinced with your answer!
Though, I know you can't justify option B.

A is correct.

Why D is not a correct answer? I think avg is the same, and the withdraw rate of students in online >> (much higher) withdraw rate of students in classroom --> more students fail in online classes, but they are still counted when calculating avg --> to lift up the avg of online students, there must be some students who score much higher than classroom students do, hence D.

OA is A, but I can't justify why D is not correct.

given,

based on information give in the question,
if people who did not withdraw are excluded in avg grade calculation, the avg grade is higher for online students than for classroom based students.
From this we cannot conclude that number of people who got best grades are more in online students for sure. Because we just know only average. We can have more students who got best grades in classroom based students and still have less average grade than online students. Hence it can't be D, because high average doesn't mean you will have large numbers in that set.

user123321

D is incorrect because it isn't necessarily true that the students taking online courses scored the highest grades. These students just scored higher on average...you have to notice the difference between D and A.

clean A here giving the exact reason.