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Senior Manager
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In a certain senior class, 75 percent of the male students [#permalink]
 08 Apr 2006, 09:50
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In a certain senior class, 75 percent of the male students and 80 percent of the female students have applied to college. What fraction of the students in the senior class are male?
1. There are 840 students in the senior class
2. 75 percent of the students in the senior class have applied to college
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statement 1 ... nothing much here
statement 2 gives us .75x(where x is the number of males)+.80y(where y is the number of females)=.75 z( z is x+y or total number of students )
.75x+.80y=.75z we can write y as y=z-x then we get
.75x+.80z-.80x=.75z ... we need to solve for (x/z) and this could be done
but this only gives us the fraction of the males which applied to college ... we still dont know about the ones that didnt..
am i missing something ?
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I just got this same question in GMATPrep. I put E. We need to know the percentage of students that are male to answer this question (at least that's what I thought), but we don't. The OA is B, but that made no sense to me.
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jcgoodchild wrote: I just got this same question in GMATPrep. I put E. We need to know the percentage of students that are male to answer this question (at least that's what I thought), but we don't. The OA is B, but that made no sense to me.
jcgoodchild,
trick here is its asking ratio of number male students to total number of students. So we don't need A because we can replace female students by total students - Male students.
Hope this will help.
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gmat_crack can you please solve this question fully.
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GMAT_Crack -- I realized what the question is asking. I had written out a whole post explaining the issue when I think I stumbled on the answer.
Ok, so we want to find the percentage of students who are male. We know a couple of things. 72% of males applied to college and 80% of females applied to college, and from B we know that this is equal to 75% of the student body.
(.72m + .8f) / (m+f) = .75
To your point, they want the ratio of male to femal students.
.72m + .8f = .75m + .75f
.05f = .03m
m/f = .05/.03 = 5/3
So the fraction of male students is 5/8 ths. Sound right?
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m+f = t (total) ----(i)
.75m + .8f = .75t ----(ii)
Divide (i) by z
m/t + f/t = 1 ------(iii)
divide (ii) also by "t" you get the value of f/t = 1- m/t
So B is enough 'cos you are asked for the portion of the males in the total class but not the # os males....
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jcgoodchild wrote: GMAT_Crack -- I realized what the question is asking. I had written out a whole post explaining the issue when I think I stumbled on the answer.
Ok, so we want to find the percentage of students who are male. We know a couple of things. 72% of males applied to college and 80% of females applied to college, and from B we know that this is equal to 75% of the student body.
(.72m + .8f) / (m+f) = .75
To your point, they want the ratio of male to femal students.
.72m + .8f = .75m + .75f
.05f = .03m
m/f = .05/.03 = 5/3
So the fraction of male students is 5/8 ths. Sound right?
If you use .75 as given in the question instead of .72 you won't get a ratio!!
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IMO, what we need is % of male students in the senior class. (fraction)
Let's assume there are 100 students in senior class.
Then,
0.75x + 0.8(100-x) = 0.75
We can solve for "x", which in itself is a fraction (or percent), So "B".
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jcgoodchild wrote: GMAT_Crack -- I realized what the question is asking. I had written out a whole post explaining the issue when I think I stumbled on the answer.
Ok, so we want to find the percentage of students who are male. We know a couple of things. 72% of males applied to college and 80% of females applied to college, and from B we know that this is equal to 75% of the student body.
(.72m + .8f) / (m+f) = .75
To your point, they want the ratio of male to femal students.
.72m + .8f = .75m + .75f
.05f = .03m
m/f = .05/.03 = 5/3
So the fraction of male students is 5/8 ths. Sound right?
Hey dude,
You are calculating the ratio of m/f, but we need here m/T where T is the total number of students.
so T = m + f
--> f = T-m
Now in equation in blue, replace f = t-m
------> [ .72m + .8(T-m)] / T = .75
from this we need to get m/T.
---------> .8 - .08*m/T = .75
---------> .05 = .08*m/T
---> m/T = 5/8
Hope this will help everyone.
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vivek123 wrote: IMO, what we need is % of male students in the senior class. (fraction)
Let's assume there are 100 students in senior class.
Then,
0.75x + 0.8(100-x) = 0.75
We can solve for "x", which in itself is a fraction (or percent), So "B".
If you solve for x you get a value that is greater than 100 students which is not correct.
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gmat_crack wrote: jcgoodchild wrote: GMAT_Crack -- I realized what the question is asking. I had written out a whole post explaining the issue when I think I stumbled on the answer.
Ok, so we want to find the percentage of students who are male. We know a couple of things. 72% of males applied to college and 80% of females applied to college, and from B we know that this is equal to 75% of the student body.
(.72m + .8f) / (m+f) = .75
To your point, they want the ratio of male to femal students.
.72m + .8f = .75m + .75f
.05f = .03m
m/f = .05/.03 = 5/3
So the fraction of male students is 5/8 ths. Sound right? Hey dude, You are calculating the ratio of m/f, but we need here m/T where T is the total number of students. so T = m + f --> f = T-m Now in equation in blue, replace f = t-m ------> [ .72m + .8(T-m)] / T = .75 from this we need to get m/T. ---------> .8 - .08*m/T = .75 ---------> .05 = .08*m/T ---> m/T = 5/8 Hope this will help everyone. and you cannot deduce the fraction if you follow that equation
Last edited by jodeci on 08 Apr 2006, 22:16, edited 1 time in total.
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jodeci wrote: vivek123 wrote: IMO, what we need is % of male students in the senior class. (fraction)
Let's assume there are 100 students in senior class.
Then,
0.75x + 0.8(100-x) = 75
We can solve for "x", which in itself is a fraction (or percent), So "B". If you solve for x you get a value that is greater than 100 students which is not correct. oops, i made a mistake....corrected in red.
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vivek123 wrote: jodeci wrote: vivek123 wrote: IMO, what we need is % of male students in the senior class. (fraction)
Let's assume there are 100 students in senior class.
Then,
0.75x + 0.8(100-x) = 75
We can solve for "x", which in itself is a fraction (or percent), So "B". If you solve for x you get a value that is greater than 100 students which is not correct. oops, i made a mistake....corrected in red. Still not right, you get 100 for x which is the same as the number you chose for all students meaning female students are zero.
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trivikram wrote: m+f = t (total) ----(i)
.75m + .8f = .75t ----(ii)
Divide (i) by z
m/t + f/t = 1 ------(iii)
divide (ii) also by "t" you get the value of f/t = 1- m/t
So B is enough 'cos you are asked for the portion of the males in the total class but not the # os males....
Agree with analysis B is enough, though I ended up selecting E at first glance...
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I keep getting m/t = 1, which makes little sense to me. It seems that everyone is getting this ratio too. Perhaps this is truly the answer. I've been scouring my calculation for mistakes but everything I have down is logical. I don't think there are any females in this school....
I've tried it through formulas and charts. Everything points to 0 females and all males. Hell, you can even use the 1st statement they give you and try it out with that. It'll give you 840 males.
Good luck...
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macca wrote: In a certain senior class, 75 percent of the male students and 80 percent of the female students have applied to college. What fraction of the students in the senior class are male?
1. There are 840 students in the senior class
2. 75 percent of the students in the senior class have applied to college
the question seems poorly structured for me because if there are male and female, both, students in the college, 75 percent of the male students and 80 percent of the female comprise more than 75% of total.
but if 75 percent of the male students and 80 percent of the female comprise more than 75% of total, then thre are only male students. so the fraction of male student is 1 (or 100%).
lets suppose total = 100
male = x
0.75x + 0.8(100-x) = 75
0.75x + 80 -0.8x = 75
0.75x -0.8x = 75-80
0.05x = 5
x = 100
if so, B is enough...
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Here is my take on this -
using the same convention, x - male, y - female, T - total
Condition1 : Doesn't give us anything.
Condition2 :
0.75 x + 0.80y = 0.75T - where T = x + y
=> 0.75x + (0.75 + 0.05) y = 0.75T
=> 0.75(x+y) + 0.05y = 0.75T
=> 0.75T + 0.05y = 0.75T
=> y = 0, i.e. there are no females in the class. So what fraction of the students are male, 100%.
Hence B.
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yeah, but it's from gmatprep!!
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hehe this problem sucks  the only reason i would think C is because i kept getting 0 females ... oh well hope i dont get something this silly on my test
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close
