Probability and Combinatorics-MGMAT Q

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Probability and Combinatorics-MGMAT Q

by fk27 » Tue Jul 19, 2011 5:44 am
Source:MGMAT

Five A-list actresses are vying for the three leading roles in the new film, "Catfight in Denmark".
The actresses are Julia Robards, Meryl Strep, Sally Fieldstone, Lauren Bake-all and Hallie Strawberry. Assuming that no actress has any advantage in getting any role, what is the probability that Julia and Hallie will star in the film together?

What I want to know is how to solve this problem using combinatorics. The solution in the guide is helpful, but only for problems in which we are dealing with small numbers because what it suggests is to write out all the possibilities. First off, is this type of problem a combination problem or permutation? Second, how would it be solved if, say the numbers were different, perhaps 10 actresses (A,B,C,D,E,F,G,H,I,J) vying for spots in a 7 person film, what is the probability that A,C,E,G,and I star together?
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by GMATGuruNY » Tue Jul 19, 2011 6:20 am
fk27 wrote:Source:MGMAT

Five A-list actresses are vying for the three leading roles in the new film, "Catfight in Denmark".
The actresses are Julia Robards, Meryl Strep, Sally Fieldstone, Lauren Bake-all and Hallie Strawberry. Assuming that no actress has any advantage in getting any role, what is the probability that Julia and Hallie will star in the film together?

What I want to know is how to solve this problem using combinatorics. The solution in the guide is helpful, but only for problems in which we are dealing with small numbers because what it suggests is to write out all the possibilities. First off, is this type of problem a combination problem or permutation? Second, how would it be solved if, say the numbers were different, perhaps 10 actresses (A,B,C,D,E,F,G,H,I,J) vying for spots in a 7 person film, what is the probability that A,C,E,G,and I star together?
I posted a solution here:

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by winniethepooh » Tue Jul 19, 2011 7:28 am
The probably of selecting any 3 actresses from 5 for the role is 5C3=10.
Number of ways you can have Julia and Hallie together along with the 3rd actresses from a pool of 3 actress=3C1=3

So i guess the probability of the given event will be 3/10.

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by fk27 » Tue Jul 19, 2011 9:20 am
Hey guys, thanks for your comments. So is the answer to my 2nd question 1/12?