Each of the 30 students in a class is either male or female, : GMAT Data Sufficiency (DS)
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# Each of the 30 students in a class is either male or female,

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Manager
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Each of the 30 students in a class is either male or female, [#permalink]

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21 Sep 2009, 17:32
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65% (hard)

Question Stats:

62% (02:18) correct 38% (01:49) wrong based on 140 sessions

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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.

Source: Jeff Sackmann's GMAT Extreme Challenge
[Reveal] Spoiler: OA

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Last edited by powerka on 22 Sep 2009, 11:20, edited 1 time in total.
Manager
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Re: Probability Problem - Extreme Challenge - Each of the 30 ... [#permalink]

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21 Sep 2009, 18:36
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We have to find the following probability:

P(Female or Brown Hair)=P(Female)+P(Brown hair)-P(Female with brown hair)

Statement 1 - gives the value of P(Female with brown hair)=10% but we do not know P(Female) and P(Brown hair).
Statement 2 - states that P(Female)-P(Brown hair)=25%. not sufficient since we do not know P(female with brown hair) and we do not know either P(female) or P(brown hair)

Combined - still not sufficient. We need to know either P(Female) or P(Brown hair) in order to solve for P(Female or Brown hair)

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Re: Probability Problem - Extreme Challenge - Each of the 30 ... [#permalink]

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21 Sep 2009, 20:28
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Expert's post
This question is, mathematically speaking, essentially identical to a GMATPrep problem:

www.beatthegmat.com/gmat-prep-q-8-proba ... t4890.html
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Re: Probability Problem - Extreme Challenge - Each of the 30 ... [#permalink]

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22 Sep 2009, 11:08
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eh! I was wondering what does 0:10 and 0:25 mean? : means . here...guess the poster must change the symbols, its confusing.
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Re: Probability Problem - Extreme Challenge - Each of the 30 ... [#permalink]

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22 Sep 2009, 11:20
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Economist wrote:
eh! I was wondering what does 0:10 and 0:25 mean? : means . here...guess the poster must change the symbols, its confusing.

Typo. Its 0.1 and 0.25. Will edit.
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Re: Each of the 30 students in a class is either male or female, [#permalink]

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29 Jun 2013, 02:31
i chose E.
from first statement we can deduce there are 3 female with brown hair (0.1=1/10=3/30)
but v can neither find out no. of females(blonde+red+brown) nor no. of students with brown hair (female + male). not sufficient

2nd statement
female/30 - brown/30=0.25=1/4=15/60
hence 2female-2brown = 15
2 variables in one equation. not sufficient

even together v cant find the solution.
so E
temme if i did anything wrong
cheers
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Re: Each of the 30 students in a class is either male or female, [#permalink]

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29 Jun 2013, 02:51
powerka 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.

Source: Jeff Sackmann's GMAT Extreme Challenge

"Stolen" GMAT Prep question:
Quote:
Each of the 25 balls in a certain box is either red, blue or white and has a number from 1 to 10 painted on it. If one ball is to be selected at random from the box, what is the probability that the ball selected will either be white or have an even number painted on it?

(1) The probability that the ball will both be white and have an even number painted on it is 0

(2) The probability that the ball will be white minus the probability that the ball will have an even number painted on it is 0.2

Discussed here: each-of-the-25-balls-in-a-certain-box-is-either-red-blue-or-99044.html
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Re: Each of the 30 students in a class is either male or female,   [#permalink] 29 Jun 2013, 02:51
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