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what probability

by maihuna » Tue Mar 15, 2011 12:17 pm
Each of the 30 students in a class is either male or female, and
has blonde, brown, or red hair. If one student is to be randomly
selected from the class, what is the probability that the student
will either be female or have brown hair?
(1) The probability that the student will both be female and
have brown hair is 0:1.
(2) The probability that the student will be female minus the
probability that the student will have brown hair is 0:25.
Charged up again to beat the beast :)
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Source: — Data Sufficiency |
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by force5 » Tue Mar 15, 2011 1:52 pm
wondering if 0:1 and 0:25 is a typo or its actually 0.1 and 0.25 plz confirm
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by HSPA » Wed Mar 16, 2011 1:17 am
Let F - number of female
Bh - number of brown hair

Out of 100 we have P(F n Bh) = 10
P(F) - P(Bh) = 25

what is P(F u Bh) = P(F)+P(Bh)-P(F n Bh)??

I am not able to solve this... Is it E??
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by sanju09 » Wed Mar 16, 2011 1:39 am
maihuna wrote:Each of the 30 students in a class is either male or female, and
has blonde, brown, or red hair. If one student is to be randomly
selected from the class, what is the probability that the student
will either be female or have brown hair?
(1) The probability that the student will both be female and
have brown hair is 0:1.
(2) The probability that the student will be female minus the
probability that the student will have brown hair is 0:25.

Although there are more than two categories in the stem that describe the 30 students, but still the question chiefly deals with only two of those categories namely female (say F) and those who have brown hair (say B), with T = 30 as the total.

What is P (F∪B)?

(1) P (F ∩B) = 0.1 cannot help us answer P (F∪B) as P (F∪B) = P (F) + P (B) - P (F ∩B). Insufficient

(2) P (F) - P (B) = 0.25 is nowhere useful in the expression P (F) + P (B) - P (F ∩B). Insufficient

Taken together, no algebra can uniquely find P (F) + P (B) from P (F) - P (B) = 0.25. [spoiler]Still insufficient


E[/spoiler]
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