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PS: Boy & Girl. 600-700 Ranking

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lexis
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PS: Boy & Girl. 600-700 Ranking [#permalink] New post   29 Aug 2008, 00:10
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A
B
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D
E

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The given information seems to be excessive. We do not need all constrains to solve problem.



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Re: PS: Boy & Girl. 600-700 Ranking [#permalink] New post   29 Aug 2008, 01:09
Ba/Ga = 3/4

Bb/Gb = 4/5

(Ba+Bb)/(Ga+Gb) = 17/22

(3Ga-2)/(Ga-1) = 34/11

Ga = 12

What was excessive and what is your approach?
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Re: PS: Boy & Girl. 600-700 Ranking [#permalink] New post   29 Aug 2008, 01:29
i think that this is where diff thinking can make a diff on the GMAT...
B:G ratio is 17:22.
this means what????
b=17x
G=22x or girls = 22,44,66,88 etc...

and Ga = Gb+2 (Ga - girls in A)
or Gb=Ga-2

from the ans choices. select that no. for girls in A, and so the girls in B will be 2 less than that. when these two are added they should be a multipe of 22.
only 12 satisfies this ...
so ans =E
time taken= 1min 50 sec..
(BUT IS THE ANS RIGHT???)
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Re: PS: Boy & Girl. 600-700 Ranking [#permalink] New post   29 Aug 2008, 08:20
LM wrote:
Ba/Ga = 3/4

Bb/Gb = 4/5

(Ba+Bb)/(Ga+Gb) = 17/22

(3Ga-2)/(Ga-1) = 34/11

Ga = 12

What was excessive and what is your approach?


We do not need the information shows 17/22 ratio.
I got 12 as well.
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Re: PS: Boy & Girl. 600-700 Ranking [#permalink] New post   29 Aug 2008, 08:25
lexis wrote:


The given information seems to be excessive. We do not need all constrains to solve problem.


Ba/Ga = 3/4
Bb/Gb = 4/5
(Ba + Bb)/(Ga + Gb) = 17/22

Bb = Ba - 1
Gb = Ga - 2

(2Ba - 1)/(2Ga - 2) = 17/22
Ba = (3/4)Ga

(2*(3/4)*Ga - 1)/(2Ga - 2) = 17/22
22*2*(3/4)*Ga - 22 = 17*2*Ga -34
33Ga - 22 = 34Ga - 34
Ga = 12
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Re: PS: Boy & Girl. 600-700 Ranking [#permalink] New post   31 Aug 2008, 09:25
E... Agreed

I solved by back-solving, just plug in values to meet the conditions from the stem, 12 is the obvious choice.


If 12 girls in A then 9 boys in A

If 9 boys in A then 8 boys in B

If 12 girls in A then 10 girls in B

9+8=17
12+10=22

ratio =17/22

Time take - 45 seconds (varies based on which answer you select to back-solve, some might initially select a wrong answer, but is should be easy to tell at an early stage that its wrong)
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Re: PS: Boy & Girl. 600-700 Ranking [#permalink] New post   31 Aug 2008, 18:57
Expert Reply
The information has one excessive fact anyway, but with those answer choices, the problem is absolutely straightforward:

We're told that class B has two fewer girls than class A. From the answer choices, class B must have 6, 7, 8, 9 or 10 girls. In class B, the ratio of boys to girls is 4 to 5. This guarantees that the number of girls in class B is divisible by 5. So the answer must be E, 12, because only 12-2 = 10 gives a multiple of 5.

So with those answer choices, the rest of the information in the question is completely unnecessary. E. What's the source?



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Re: PS: Boy & Girl. 600-700 Ranking [#permalink]
31 Aug 2008, 18:57
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