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DS question on prep 1

by fangtray » Sun Apr 08, 2012 1:41 am
What fraction of this year's graduating students at a certain college are males?

1. of this year's graduating students, 33% of the males and 20% of the females transferred from another college

2. Of this year's graduating stuents, 25% transferred from another college

I got this question right as I chose C, but I was wondering on questions such as these, which is the best way to solve?

Do we make a table with Males,Females, Transfer and not transfer or do we use algebra?

If I use algebra, is this approach correct?
x=male
y=female

.33x + .20y = .25(x+y)

.08x = .05y

8x=5y

x/y = 5/8


fraction of graduating students at a certain college is x/(x+y) so 5/13
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by Pharo » Sun Apr 08, 2012 2:04 am
The best way is to do it algebraically as you did it :)
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by GMATGuruNY » Sun Apr 08, 2012 4:16 am
=
fangtray wrote:What fraction of this year's graduating students at a certain college are males?

1. of this year's graduating students, 33% of the males and 20% of the females transferred from another college

2. Of this year's graduating stuents, 25% transferred from another college

I got this question right as I chose C, but I was wondering on questions such as these, which is the best way to solve?

Do we make a table with Males,Females, Transfer and not transfer or do we use algebra?

If I use algebra, is this approach correct?
x=male
y=female

.33x + .20y = .25(x+y)

.08x = .05y

8x=5y

x/y = 5/8


fraction of graduating students at a certain college is x/(x+y) so 5/13
Your solution is perfect for a PS problem.
But this is a DS problem.
You shouldn't actually SOLVE for the fraction but should simply recognize that you COULD, pick C, and move on.
Check my posts here:

https://www.beatthegmat.com/question-on- ... tml#365673

In my first post, I suggest you how you could determine the correct answer here without doing any actual math.
In my second post, I suggest alligation, which you might find faster and easier than algebra.
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by fangtray » Mon Apr 09, 2012 5:51 am
GMATGuruNY wrote:=
fangtray wrote:What fraction of this year's graduating students at a certain college are males?

1. of this year's graduating students, 33% of the males and 20% of the females transferred from another college

2. Of this year's graduating stuents, 25% transferred from another college

I got this question right as I chose C, but I was wondering on questions such as these, which is the best way to solve?

Do we make a table with Males,Females, Transfer and not transfer or do we use algebra?

If I use algebra, is this approach correct?
x=male
y=female

.33x + .20y = .25(x+y)

.08x = .05y

8x=5y

x/y = 5/8


fraction of graduating students at a certain college is x/(x+y) so 5/13
Your solution is perfect for a PS problem.
But this is a DS problem.
You shouldn't actually SOLVE for the fraction but should simply recognize that you COULD, pick C, and move on.
Check my posts here:

https://www.beatthegmat.com/question-on- ... tml#365673

In my first post, I suggest you how you could determine the correct answer here without doing any actual math.
In my second post, I suggest alligation, which you might find faster and easier than algebra.
Thank you for the help! I am a little confused with allegation though, I was wondering if you could show me how if the problem was a PS problem, could be solved with the following 2 formulas:

weighted avg: [(a)*(data pt)/(a+b)] + [(b)*(data pt)/(a+b)]

and

(percent difference between smaller solution and desired solution) * (amount of smaller solution) = (percent difference between larger solution) * (amount of stronger solution)

both of these seem very similiar to alligation, but i'm not sure how you solved for the ratio with just knowing the ratio of transfer students. using 25% - 20% and 35%-20%. Im also not sure how for solving for Men, why you used 25% - women % and vice versa.

thanks so much for all the help you given me on this post and all other posts!
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