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Percentages/Weighted Average:

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mohit.khemu
 Post subject: Percentages/Weighted Average:
 Post Posted: Mon Apr 25, 2011 9:00 am 
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Students


Posts: 16
What fraction of this year's graduating students at a certain college are males?
1- of this year's graduating student, 33 % of the males and 20% of females transferred from another college.
2- of this year's graduating students 25% transferred from another college.

OA:C
Ron, this is from one of your other posts:
note that this is a WEIGHTED AVERAGES problem.
on weighted averages problems, if you know any 2 of the following 3, then you can find the third one:
1. the ratio of 'weights' of the different quantities
2. the values of the quantities
3. the weighted average

Can we do the above posted problem also by this concept? I had two similar questions in the same prep.

Thanks in anticipation.
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RonPurewal
 Post subject: Re: Percentages/Weighted Average:
 Post Posted: Wed Apr 27, 2011 5:06 am 
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ManhattanGMAT Staff


Posts: 7146
mohit.khemu wrote:
What fraction of this year's graduating students at a certain college are males?
1- of this year's graduating student, 33 % of the males and 20% of females transferred from another college.
2- of this year's graduating students 25% transferred from another college.

OA:C
Ron, this is from one of your other posts:
note that this is a WEIGHTED AVERAGES problem.
on weighted averages problems, if you know any 2 of the following 3, then you can find the third one:
1. the ratio of 'weights' of the different quantities
2. the values of the quantities
3. the weighted average

Can we do the above posted problem also by this concept? I had two similar questions in the same prep.

Thanks in anticipation.


yes.
the question is asking for the fraction of males; knowing the fraction of males is equivalent to knowing the ratio of males to females. therefore, the question is asking for #1 above.
statement 1 gives the values of the quantities (#2 above) and statement 2 gives the weighted average (#3 above), so, together, the are sufficient.
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mohit.khemu
 Post subject: Re: Percentages/Weighted Average:
 Post Posted: Wed Apr 27, 2011 10:42 am 
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Students


Posts: 16
Thanks a lot. Really appreciate it.
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jnelson0612
 Post subject: Re: Percentages/Weighted Average:
 Post Posted: Sat Apr 30, 2011 1:13 pm 
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ManhattanGMAT Staff


Posts: 1857
:-)

_________________
Jamie Nelson
ManhattanGMAT Instructor
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ganeshgajamugan
 Post subject: Re: Percentages/Weighted Average:
 Post Posted: Wed May 09, 2012 11:27 am 
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Course Students


Posts: 8
if you know any 2 of the following 3, then you can find the third one:
1. the ratio of 'weights' of the different quantities
2. the values of the quantities
3. the weighted average

I understand everything except the scenario when you are given the ratio of weights and the weighted average. How does one go about finding the values of the quantities? I am able to find the ratio of the quantities, but cannot find the exact quantities? I solved some questions backwards and tried omitting the values and seeing if they were solvable, but I ended up with many possibilities. However, the ratio of the values of quantities could be calculated... Could you confirm that the actual values of the quantities cannot be calculated or if they can, can you please explain how?
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RonPurewal
 Post subject: Re: Percentages/Weighted Average:
 Post Posted: Thu May 17, 2012 5:32 am 
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ManhattanGMAT Staff


Posts: 7146
ganeshgajamugan wrote:
if you know any 2 of the following 3, then you can find the third one:
1. the ratio of 'weights' of the different quantities
2. the values of the quantities
3. the weighted average

I understand everything except the scenario when you are given the ratio of weights and the weighted average. How does one go about finding the values of the quantities? I am able to find the ratio of the quantities, but cannot find the exact quantities? I solved some questions backwards and tried omitting the values and seeing if they were solvable, but I ended up with many possibilities. However, the ratio of the values of quantities could be calculated... Could you confirm that the actual values of the quantities cannot be calculated or if they can, can you please explain how?


ya, they can't. i was pretty much improvising when i wrote that, haha.

if you have the weights and the weighted average, what you can find is the relative distances away from the weighted average.
for instance, if 'p' has twice the weight of 'q' and the weighted average is 20, then 'p' must be exactly half as far away from 20 as 'q' (and in the opposite direction).
so, for instance, if q = 30 in this situation, then p = 15. or, if p = 30, then q = 0.

that was a stupid moment. heh.
it's interesting that it took about 2.5 years for someone to notice that something was wrong with that statement (which i think i posted in late 2009). nice catch.
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