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Math Help - random variable probability

  1. #1
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    random variable probability

    a train from jackson city to state city is scheduled to arrive at 8:07 am every weekday morning. the probability that the train arrives on time is .90

    Suppose twenty weekdays are randomly selected.

    must find the probability that the train will arrive on time on at most fifteen days.

    then whats the probability the train will arrive on time on at least days.

    then find the expected number of days the train arrives on time.

    so if the train arrives on time on atleast fifteen days what is the probability that it arrives on time on all twenty of the days?

    thanks for any help with this long word problem.
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  2. #2
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    Quote Originally Posted by rcmango View Post
    a train from jackson city to state city is scheduled to arrive at 8:07 am every weekday morning. the probability that the train arrives on time is .90

    Suppose twenty weekdays are randomly selected.

    must find the probability that the train will arrive on time on at most fifteen days.

    then whats the probability the train will arrive on time on at least days.

    then find the expected number of days the train arrives on time.

    so if the train arrives on time on atleast fifteen days what is the probability that it arrives on time on all twenty of the days?

    thanks for any help with this long word problem.
    Let X be the random variable number of days the train arrives on time.

    X ~ Binomial(n = 20, p = 0.9)

    If you need more help please show what you've done and say where you get stuck.
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