Unformatted text preview: 6 1 )( 94 K1 ) ( 100 K ) . By trial and error we ﬁnd P ( X = 0 or 1) = . 10220 for K = 50 and P ( X = 0 or 1) = . 09331 for K = 51. So the sample size must be at least 51. 3.3 In the seven seconds for the event, no car must pass in the last three seconds, an event with probability (1p ) 3 . The only occurrence in the ﬁrst four seconds, for which the pedestrian does not wait the entire four seconds, is to have a car pass in the ﬁrst second and no other car pass. This has probability p (1p ) 3 . Thus the probability of waiting exactly four seconds before starting to cross is [1p (1p ) 3 ](1p ) 3 ....
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 Spring '12
 Dr.Hackney
 Statistics, Automobile, Walking, The Pedestrian

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