jury

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jury

by GmatKiss » Mon May 14, 2012 6:38 pm
If a jury of 12 people is to be selected randomly from a pool of 15 potential jurors, and the jury pool consists of 2/3 men and 1/3 women, what is the probability that the jury will comprise at least 2/3 men?

a. 24/91
b. 5/91
c. 2/3
d. 67/91
e. 84/91
Source: — Problem Solving |

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by eagleeye » Mon May 14, 2012 7:19 pm
Hi GMATKiss:

This is how I solved it.

12 people are to be selected from 15, no. of ways = 15C12.
Now of these 15 people, 2/3 are men, so men = 2/3*15 = 10, hence women = 5.

Now we need to choose 12 people such that at least 2/3 of the 12 are men, that is 2/3*12= 8. So at least 8 should be men. So there can be maximum of 4 women. Now the max no. of women in our pool of 15 = 5. Therefore, if we can eliminate this particular case (when we choose all 5 women), then there are always at least 8 men.

Now when 5 women are chosen, no. of ways to choose the 12 people jury = 5C5*10C7. (since the other seven have to come from the remaining 10 men).

Therefore, the required probability is 1 - 5C5*10C7/(15C12) = 1 - 10*9*8/(15*14*13) = 1 - 24/91 = 67/91.

Hence D is the correct choice.

Let me know if this works :)

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by Stuart@KaplanGMAT » Mon May 14, 2012 11:08 pm
Hi!

I gave a detailed explanation to this question here:

https://www.beatthegmat.com/i-suck-at-pr ... t8927.html
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Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

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