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Unformatted text preview: Two events A and B are independent if P(BA) = P(B). Example 2: You come home late one night from being out (I presume you were studying, but your call!) and you are struggling to find the correct key to your apartment. You have 5 keys. What is the probability that you find the correct key on your second try, assuming you don't repeat keys? Let A 1 = first key works and A 2 = second key works. The P(A 1 ) = 1/5 and P(A 2 ) = = 1/4. This is correct since after you try the first key and it does not work you are left with 4 keys to try. Now to find the probability that you try exactly two keys is the "probability that the first key does not work and the second key does work." Or by probability expressions this is written: Surprisingly, the probability of using exactly 2 keys = probability of exactly 3 keys = probability of exactly 4 keys = probability of exactly 5 keys! Bet your friends on that!...
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 Spring '11
 AndyRegards
 Conditional Probability, Probability

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