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# In a certain senior class, 72 percent of the male students and 80 perc

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Intern
Joined: 11 Jul 2010
Posts: 27
In a certain senior class, 72 percent of the male students and 80 perc [#permalink]

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17 Sep 2010, 21:48
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Difficulty:

55% (hard)

Question Stats:

60% (00:24) correct 40% (01:08) wrong based on 30 sessions

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In a certain senior class, 72 percent of the male students and 80 percent of the female students have applied to college. What fraction of the students in the 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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Math Expert
Joined: 02 Sep 2009
Posts: 45498
Re: In a certain senior class, 72 percent of the male students and 80 perc [#permalink]

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17 Sep 2010, 21:54
In a certain senior class, 72 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?

This is weighted average question.

Q: $$\frac{m}{m+f}=?$$

(1) There are 840 students in the senior class --> $$m+f=840$$. Stem info is useless. Not sufficient.

(2) 75 percent of the students in the senior class have applied to college --> $$0.72m+0.8f=0.75(m+f)$$ --> $$3m=5f$$ --> $$\frac{m}{f}=\frac{5}{3}$$ --> $$\frac{m}{m+f}=\frac{5}{8}$$. Sufficient.

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Re: In a certain senior class, 72 percent of the male students and 80 perc [#permalink]

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17 Sep 2010, 21:59
rgtiwari wrote:
Ina a certain senior class, 72% of the male students and 80% of the female students have applied to the college.What fractions of the students in the senior class are male?

a) There are 840 students in the senior class.
b) 75% of the stunts in the senior class have applied to the college.

We need to find what fraction of students are male in the senior class..

a-> clearly insuff
b-> 75% have applied to college
Lets take x number of male and y no of female students are thr.

so,

(72/100)X | (80/100)Y=(75/100)(X+Y)
5Y=3X

b-> sufficient..
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Re: In a certain senior class, 72 percent of the male students and 80 perc [#permalink]

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09 Nov 2010, 06:07
1
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Expert's post
anilnandyala wrote:
in a certain class 72% of the male students & 80% of the female students have applied to college what fraction of the students in the senior college are male?
1 there are 840 students in the senior class
2 75% students in the senior class have applied to the college

(I am assuming that 'senior college' in question stem is the same as 'senior class')
This is a question of weighted averages.

Statement 1: Total students is 840 but we do not know how many of them are male and how many are female.

Statement 2: 75% of total have applied to college. 72% of males have applied and 80% of females have applied. The weighted average of 72% and 80% is known to be 75%.

_______________________
72% 75% 80%

Diff between 72 and 75 is 3 and that between 75 and 80 is 5 hence males:females ratio is 5:3.

Hence 5/8 of the students in senior class are males.
Statement 2 is sufficient. Answer is (B).
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Joined: 31 Oct 2011
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Re: In a certain senior class, 72 percent of the male students and 80 perc [#permalink]

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04 Jan 2012, 02:24
I know how to solve these questions on DS. I know the rule actually but dont know step by step solution so would really appreciate if someone can provide that. Thanks
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Manager
Joined: 14 Mar 2011
Posts: 75
Re: In a certain senior class, 72 percent of the male students and 80 perc [#permalink]

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04 Jan 2012, 03:49
Hi

Says M-Present Males & F-Present Females .. The statement we have senior class have 0.75M+.80F-

Total Students lot = M+F

Statement 1- M+F = 840 - Not Sufficient .. to determine fraction of M

Statement 2 - means 0.75 (M+F) = 0.75M+0.80 F

WE can calculate M & F relation

So M fraction can be workout as ------------ M/ (M+F) by converting F in terms of M from Statement 2 .

So B is right Answer
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Re: In a certain senior class, 72 percent of the male students and 80 perc [#permalink]

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04 Jan 2012, 07:53
from statement 2 we get: 5F=3M
how B is sufficient to answer: M/(M+F)?
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Re: In a certain senior class, 72 percent of the male students and 80 perc [#permalink]

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04 Jan 2012, 08:00
sorry for the last post. I got it.
Manager
Joined: 29 Jul 2011
Posts: 98
Location: United States
Re: In a certain senior class, 72 percent of the male students and 80 perc [#permalink]

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06 Jan 2012, 19:19
Hi, let me simplify this for you.

Have you read distribution charts from MGMAT word problem book? You need to form a chart like this:

Male Female Total
Applied
not Applied

Let total be 100 (100%).
Let total males = y, females = 100-y.

You get applied + Males = 0.72y (72%)
You get applied +Females = 0.80(100-y) (80%)

Rephrase: y = ?

Now, lets look at the statements.
1. Total given, no use since we don't know male/female distribution. Insuff.
2. Applied = 75% total. So, we get 0.72y + 0.8(100-y) = 75. solving gives us y. Suff

B.
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Math Expert
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Re: In a certain senior class, 72 percent of the male students and 80 perc [#permalink]

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23 Nov 2017, 08:13
In a certain senior class, 72 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 is male?

Question: $$\frac{m}{m+f}=?$$ (so we are asked about #3)

(1) There are 840 students in the senior class --> $$m+f=840$$. Useless info. Not sufficient.

(2) 75 percent of the students in the senior class have applied to college. We know 2 from the stem and 1 from this statement, sufficient to get 3. Just to illustrate: $$0.72m+0.8f=0.75(m+f)$$ --> $$3m=5f$$ --> $$\frac{m}{f}=\frac{5}{3}$$ --> $$\frac{m}{m+f}=\frac{5}{8}$$. Sufficient.

OPEN DISCUSSION OF THIS QUESTION IS HERE: http://gmatclub.com/forum/in-a-certain- ... 28279.html

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.

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Re: In a certain senior class, 72 percent of the male students and 80 perc   [#permalink] 23 Nov 2017, 08:13
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# In a certain senior class, 72 percent of the male students and 80 perc

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