OG12, diagnostic test, Q31

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tnaim: Senior | Next Rank: 100 Posts; Posts: 67; Joined: Tue Mar 16, 2010 2:06 pm; Thanked: 3 times

by tnaim » Mon Jun 28, 2010 6:13 pm

31. 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.

OAA

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Source: Beat The GMAT — Critical Reasoning | Mon Jun 28, 2010 6:13 pm

tnaim: Senior | Next Rank: 100 Posts; Posts: 67; Joined: Tue Mar 16, 2010 2:06 pm; Thanked: 3 times

by tnaim » Mon Jun 28, 2010 6:23 pm

my question is this:
let's say that Group O represents students who took the course online and that group O has 8 students who scored the following:
4 withdrew
1 failed
3 70
and let's say that group A represents students who took the course in an actual class and that group A has 8 students who scored the following:
2 withdrew
3 failed
1 75
1 65
1 70

Both groups satisfy argument conditions which are: 1) withdrawal rate of online class was much higher that that of actual class. 2) both groups have the same overall average. However, it does not follow from these two premises that Among students who did not withdraw, students enrolled in online courses got higher grades, on average, than
students enrolled in classroom-based courses. both students have an average of 70, could you please clarify
side point: i don't understand how GMAT can expect to have this question answered in 2 mins!!

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Domnu: Master | Next Rank: 500 Posts; Posts: 385; Joined: Sun May 24, 2009 3:55 pm; Thanked: 11 times; GMAT Score:740

by Domnu » Mon Jun 28, 2010 10:37 pm

Process of elimination:

B - we're talking about averages, and not pure numbers... this is out of scope (scalability purposes).
C - clearly out of scope.
D - out of scope. we can conjure cases where the students with the best grades take classroom-based courses. in particular, how many students are the best students? this is really vague.
E - totally out of scope.

Have you wondered how you could have found such a treasure? -T

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tnaim: Senior | Next Rank: 100 Posts; Posts: 67; Joined: Tue Mar 16, 2010 2:06 pm; Thanked: 3 times

by tnaim » Tue Jun 29, 2010 5:22 pm

Domnu wrote:Process of elimination:

B - we're talking about averages, and not pure numbers... this is out of scope (scalability purposes).
C - clearly out of scope.
D - out of scope. we can conjure cases where the students with the best grades take classroom-based courses. in particular, how many students are the best students? this is really vague.
E - totally out of scope.

Thank you for trying to help but your post does not help me understand whether the example I brought above invalidates option A. In fact, I followed the same process of elimination when attempting to answer the question and thought that option A was just an attempt from GMAT to switch from discussing equal average grades in two separate classes to discussing which average grade was higher for a subgroup of the main group which happens to be the focus of the question.

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