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Good DS (Data Sufficiency) questions from Official GMATPrep

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Intern
Joined: 09 Aug 2007
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Good DS (Data Sufficiency) questions from Official GMATPrep [#permalink]

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30 Sep 2007, 22:29
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Hi All,

Attached are some of the questions from GMATPrep that I got wrong. The options marked with the bold black dot in the attachment are mine and are the wrong answers. The options marked by a square blue frame are correct as these are the correct answers marked by the software. However the software does not explain why a particular choice is correct and others are wrong. I will be very grateful if some of you can help justify why the correct choice is actually correct!

Many thanks.

Attachments

DS-Set2.zip [131.66 KiB]

DS-Set1.zip [152.65 KiB]

VP
Joined: 08 Jun 2005
Posts: 1145
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02 Oct 2007, 11:29
If n and P are integers is P > 0 ?

statement I

n+1 > 0

n > -1

No info on p so insufficient.

statement II

Since n*p > 0 then either p & n are positive (i.e. -2*-3 = 6) or both negative (i.e. 2*3 = 6)

but we cannot tell which is p so insufficient.

both statements

the key to solveing this problem is to understand that n is an integers hence n > -1 can only be positive (it cannot be -1/2 or 0).

if n > 0 and n*p > 0 then p has to be > 0

sufficient

VP
Joined: 08 Jun 2005
Posts: 1145
Followers: 7

Kudos [?]: 213 [0], given: 0

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02 Oct 2007, 12:15
from stem

O is the center - hence BO and CO are both radii and BO = CO.

forming an equilateral

AB = OC (given)

statement I

COD = 60 degrees.

then AOC = 120

let ABO = BOA = x

and let OBC = BCO = y

now you can build two equations:

120+y+x = 180

2y+120-x = 180

solving

y = 2x

x = 20

y = 40

sufficient

statement II

BCO = 40 degrees

since BO = CO (see stem) then BCO is equilateral

hence OBC = 40 degrees

If OBC = BCO = 40 then ABO = 140

and since AB = OC (given) then AB = OC = BO (radii of circale).

sufficient

02 Oct 2007, 12:15
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