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3 of the hardest questions in GmatPrep!

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Intern
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3 of the hardest questions in GmatPrep! [#permalink] New post 06 Mar 2007, 04:01
Could u help me out with these 3 questions?? The OA is the one circled in blue (while the other is the one i picked =( )

These should be from the hardest ones found on GmatPrep, as i scored 50 in Quant section...

Please provide extensive explanation to the solution, cause i really don't know how to get it!!

Thanks

Riccardo
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Senior Manager
Senior Manager
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 [#permalink] New post 06 Mar 2007, 07:03
first.... well done for scoring 50....

now for the questions:
question 1:
there are 4 possible "session attendance" outcomes:
A: no session
B: morning only
C: afternoon only
D: morning and afternoon

each person of the 128 is exactly in one group.
stem tells us that group A is empty. great.
it also asks how many people are in group B....

st1 tells us that group D has 3/4 of the people.... which means the rest are divided between B and C... so is insufficient.
st2 tells us that "7/8 of the people attended the afternoon session"... what does it mean? which groups from A,B,C,D attended the afternoon session? oh... that's C and D. so C and D together holds 7/8 of the people. where can be the remaining 1/8? true... in group B, which is exactly what we wanted to know. so st2 is sufficient.

answer is B.


question number 2:
to understand your mistake just plug-in x=2 and x=-2 and see that the answer is not always 1. this same example will show you that the result is neither -1,0 nor x. so by elimination you can safely deduce that the answer is E.

question number 3:
lets denote angle QRS by a, RSQ by b, STU by c and TSU by d.
we know that a+d=90 (because it is right triangle).
we also know that c+b+x=180 or x=180-(b+c)
so we miss lots of info.
st1 and st2 are clearly insufficient alone (each one deals with one side and provide no info on the other side of the problem).
lets check them together..
from st1 we know that QRS is isosceles, which means b=(180-a)/2
from st2 we similarly infer that c=(180-d)/2
b+c = (360-a-d)/2 = 270/2 = 135 (because a+d = 90)
so x=45
hence st1,st2 together are sufficient.
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 [#permalink] New post 06 Mar 2007, 07:40
Explaination 1)

Each person must be a part of either morning or afternoon or both sessions.

7/8 of the group attended afternoon, so remaining 1/8th must be part of morning.

Because remaining 1/8 th of the group either attended morning or did not attend morning (this is not true as it is already mentioned in the statement).
  [#permalink] 06 Mar 2007, 07:40
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3 of the hardest questions in GmatPrep!

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