fraction of students

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joannabanana: Master | Next Rank: 500 Posts; Posts: 118; Joined: Sun Sep 05, 2010 10:21 am; Location: Canada; Thanked: 5 times; GMAT Score:730

fraction of students

by joannabanana » Mon Oct 11, 2010 4:00 am

What fraction of this year's graduating students at a certain college are males?

(1) Of this year's graduating class, 33 percent of the males and 20 percent of the females transferred from another college.
(2) Of this year's graduating students, 25 percent transferred from another college.

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Source: Beat The GMAT — Data Sufficiency | Mon Oct 11, 2010 4:00 am

kmittal82: Master | Next Rank: 500 Posts; Posts: 324; Joined: Mon Jul 05, 2010 6:44 am; Location: London; Thanked: 70 times; Followed by:3 members

by kmittal82 » Mon Oct 11, 2010 4:15 am

Let there be m males and f females. We need to find m/(m+f)

1) Clearly not enough

2) clearly not enough

1+2

0.33m + 0.20f = 0.25(m+f)

This gives us 8m - 5f = 0, which gives us the ratio between males and females. This is sufficient to calculate m/(m+f)

(C)

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joannabanana: Master | Next Rank: 500 Posts; Posts: 118; Joined: Sun Sep 05, 2010 10:21 am; Location: Canada; Thanked: 5 times; GMAT Score:730

by joannabanana » Mon Oct 11, 2010 7:58 am

Right, I kiiinda see it, and was somewhat on that track, but it's still not clear in my head.

Can anyone else chime in with a more thorough answer, and maybe a strategy for how to deal with these types?

I think that part of what made this difficult for me was that I found the wording confusing.

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kmittal82: Master | Next Rank: 500 Posts; Posts: 324; Joined: Mon Jul 05, 2010 6:44 am; Location: London; Thanked: 70 times; Followed by:3 members

by kmittal82 » Mon Oct 11, 2010 9:13 am

joannabanana wrote:Right, I kiiinda see it, and was somewhat on that track, but it's still not clear in my head.

Can anyone else chime in with a more thorough answer, and maybe a strategy for how to deal with these types?

I think that part of what made this difficult for me was that I found the wording confusing.

Ok, heres another shot...

Let there be a total of m males, and f females in the graduating class. Thus, total number who graduated = m+f
We need to find the fraction of males from this, which means m/(m+f)

Now, lets look at 1

33% males and 20% females = (33/100)m + (20/200)f

Now, lets look at 2

25% of total students transferred from another colleged => (25/100)(m+f) transferred from another college.

Thus

0.33m + 0.20f = 0.25(m+f)

Multiply both sides by 100

33m + 20f = 25m + 25f
=> 8m= 5f => m = (5/8)f

Now, lets see if this is enough to find m/(m+f)

= (5/8)f/[(5/8)f + f]

= (5/8)f/(13/8)f = 5/13

Hence, the ratio is 5/13.

Hope that's a bit more clear