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GMAT prep PS question

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Source: — Problem Solving |
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by DeepakR » Wed Apr 22, 2009 4:41 pm
Lets have the Total number of students as T=1000
then M= 480 and F=520.

Now M and F who are > 25 yrs are
M= 480*40/100=192
F=520*1/5=104

Hence Probability,P=192/1000 + 104/1000 = 296/1000 = 0.296=0.3 approx

D.) = 0.3

- Deepak
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by tdadic84 » Wed Apr 22, 2009 4:48 pm
are u sure???

100 students..

approx. 50 male 50 female

20 males 25+....10 females 25+

therefore...70 under 25...

therefore prob. of being selected is 70/100 = 0.70

correct me if i am wrong please...
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by lilu » Wed Apr 22, 2009 8:07 pm
I second for 0.7
40/100 of 48 male=19.2 greater than 25
20/100 of 52 female=10.4 greater than 25
19.2+10.4=29.6 greater than 25
So appr 70% is less than 25
And the probability is 70 out 100=0.7
The more you look, the more you see.
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by rossmj » Thu Apr 23, 2009 5:46 am
Answer is .70, first solution is correct except for it is solved for the probability of someone greater than 25 and the question asks for less than 25.

For a quick way use a class size of 1000
M=480; M<25=480*.6=288
F=520; F<25=520*.8=416

M+F/1000=704/1000=.704

Normally using a value of 100 works well in percent questions but when you get decimals for values when you need integers (i.e. People) just move the decimal to the right one place.
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by DeepakR » Thu Apr 23, 2009 7:36 am
Thanks Rossmj..The community Sponsors is actually partly covering the question and hence i missed the last part..thanks for correcting

-Deepak
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by gmat740 » Thu Apr 23, 2009 7:51 am
let the class strength be 100
Males = 48
Females =52

now, 40% of M are 25+
so, 60% of M less than 25

thus, 0.6*48 = 28.8 males = 29 M

Similarly,
20% of 52 F are 25+
so, 80% of 52 F are less than 25 yrs

thus,
0.8*52 = 42 F less than 25

total people less than 25 = 29M+42 F = 71

total = 100
Prob = 71/100 = 0.71

Hope this Helps
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by mike22629 » Thu Apr 23, 2009 11:11 am
Yea answer is D.

Best way to do this problem, in my opinion, is with a matrix.
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by ketkoag » Sat Apr 25, 2009 3:47 am
answer is B .70
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