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Director
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Status: Preparing for the 4th time -:(
Joined: 25 Jun 2011
Posts: 563
Location: United Kingdom
Concentration: International Business, Strategy
GMAT Date: 06-22-2012
GPA: 2.9
WE: Information Technology (Consulting)
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Kudos [?]: 374 [0], given: 217

GMAT Tests User
Exams [#permalink] New post 18 Nov 2011, 13:02
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

33% (00:00) correct 67% (01:39) wrong based on 3 sessions
The average score of x number of exams is y. When an additional exam of score z is added in, does the average score of the exams increase by 50%?
(1) 3x = y
(2) 2z - 3y = xy

For me its E. Can someone please confirm?
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E.

MGMAT 1 --> 530
MGMAT 2--> 640
MGMAT 3 ---> 610 :-(

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Joined: 08 Jan 2009
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Re: Exams [#permalink] New post 19 Nov 2011, 04:40
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Restate the question as variables:

is (xy + z)/(x+1) = 1.5y?
xy + z = 1.5xy + 1.5y
.5xy = z - 1.5y
xy = 2z - 3y



1) No idea what number z is - NS
2) 2z - 3y = xy - Sufficient as per restatment

B

Another way to think of this is to try some numbers. Clearly A is insufficient we need to know something about z, but with 2), you could try something like the following:

assume x = 1, y = 1, by 2) z must = 2
average before: 1, average after: 3 / 2 = 1.5. Exactly 50% increase.

assume x = 2, y = 4, by 2) z = 10
average before: 8 / 2 = 4, average after 18 / 3 = 6. Exactly 50% increase.

Seems safe to go with B.
_________________

My Debrief

Re: Exams   [#permalink] 19 Nov 2011, 04:40
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