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Math Help - simple probability question - need help

  1. #1
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    simple probability question - need help

    Westjet had the second best on-time arrival rate of all airlines in North America, just behind Hawaiian airlines. The average for all North America airlines is 70%. In a particular 90 day rolling average the on-time arrival rate for Westjet was 80 %.
    Consider a test conducted by randomly selecting 9 Westjet flights and observing whether they arrive on time.
    Find the probability that at least 3 flights arrive late.
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  2. #2
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    Quote Originally Posted by proski117 View Post
    Westjet had the second best on-time arrival rate of all airlines in North America, just behind Hawaiian airlines. The average for all North America airlines is 70%. In a particular 90 day rolling average the on-time arrival rate for Westjet was 80 %.
    Consider a test conducted by randomly selecting 9 Westjet flights and observing whether they arrive on time.
    Find the probability that at least 3 flights arrive late.
    Binomial distribution problem. The number ontime from a sample of nine has a binomial distrinution B(9,0.8), so you want:

     <br />
p=\sum_{i=3}^9b(i;9,0.8)=1-(b(0;0,0.8)+b(1;9,0.8)=b(2;9,0.8))<br />

    CB
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