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Probability Question (PP CD)

Expert replies
by jcan-gmatter » Mon Oct 01, 2007 11:34 am
Hello all,

Got the following question wrong on the practice powerprep test. After looking some more at the question, I worked out the following. Is it correct?

Question
In the graduating class of a certain college, 48% of the students are male and 52% are female. In this class 40% of the male and 20% of the female students are 25 years old or older. If one student in the graduating class is randomly selected, approximately what is the probability that he or she will be less than 25 years old?

A. 0.90
B. 0.70
C. 0.45
D. 0.30
E. 0.25

Working
P (M & < 25)
=> P(M) * P( < 25)
=> 0.48 * 0.60
=> 0.208

P (F & < 25)
=> P(F) * P(<25)
=> 0.52 * 0.80
=> 0.416

Therefore, P(<25) = 0.208 + 0.416 = 0.704.

Hence, answer is B.

Is the above working correct?
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Source: — Problem Solving |

by mtg123 » Mon Oct 01, 2007 12:24 pm
Your approach is correct.
But my approach is

% of students > 25 = 40/100(48) + 20/100(52)
= 29.6 = 30 approx

So % of students <25 = 100- 30 = 70
Probality of picking one student < 25 = 70C1/100C1 = 70/100 = 7/10
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Thank You

by jcan-gmatter » Mon Oct 01, 2007 8:04 pm
Hey mtg123,

Thank you for that approach. Will review and determine if I can apply it to other problems that I encounter.

/Regards
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