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Thread: probability

  1. #1
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    A congested computer network has a 0.002 probability of losinga data packet and packet losses are independent events. Alost packet must be resent.
    a) What is the probability that an e-mail message with100 packets will need any resent?
    b) What is the probability that an e-mail message with 3packets will need exactly one to be resent?
    c) If 10 e-mail messages are sent, each with 100packets, what is that probability that at least one message willneed some packets to be resent?

    i know the answer for (a) is P= 1-(1-0.002)^100

    however i need some help understanding why it is so. i know the (1-0.002) is the probability that a packet is not lost. i also know that since there are 100 packets in the e-mail, that there are x^100 chances of it not being lost.

    i do not understand why (1-0.002)^100 is subtracted from 1, wouldn't this give the probability that ALL are lost?

    also, why can't you just do (probability packets lost)^100?, (0.002)^100,a and how about (b) and (c)?

  2. #2
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    Re: probability

    For part a), the required event is that "at least 1 packet out of 100 is lost"

    So you consider the complementary event "0 packet is lost", or equivalently "100 packets are sent successfully".

    b,c) are just using Binomial pmf. It is not hard after you figure out part a).

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