Binomial Distribution Formula and Concept

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EMAN: Master | Next Rank: 500 Posts; Posts: 162; Joined: Sun Aug 09, 2009 4:17 pm; Location: Minnesota; Thanked: 1 times

by EMAN » Mon Sep 21, 2009 7:10 pm

If there is an equal probability of something occuring (as in 50/50), can we always use the formula below?

N! / N! (N - X)! x (Probability)^X x (1 - Probability)^N-X

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Source: Beat The GMAT — Problem Solving | Mon Sep 21, 2009 7:10 pm

praky_rules: Senior | Next Rank: 100 Posts; Posts: 45; Joined: Wed Jun 11, 2008 4:25 pm; Thanked: 4 times; GMAT Score:730

by praky_rules » Wed Sep 23, 2009 5:50 am

Yes. You can. For two exhaustive and mutually exclusive events and for all probablilities(not necessarily equal)

For two events, A and B

P(A) + P(B) = 1, you can use the formula

Probability of X "As" in N attempts = N! / N! (N - X)! x (P(A))^X x (P(B))^N-X

For equal probablity of A and B.....for instance the coin toss. = N! / N! (N - X)! x (P(A))^N

where P(A) = .5

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