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Homework Help: Discrete Math Computer Science Question

  1. Apr 8, 2016 #1
    1. The problem statement, all variables and given/known data
    Find the probability that a randomly generated bit string of length 10 begins with a 1 or ends with a 00 if

    a)a 0 bit and a 1 bit are equally likely.
    b)The probability that a bit is a 1 is .7
    c)The probability that the ith bit is a 1 is 1/2i for i=1,2,3,...,10

    2. Relevant equations

    3. The attempt at a solution

    Since I know that the length is 10, and that the first and last two spots are already selected, I only have to worry about the middle 7 spots. A bit can only be 2 choices 0 or 1.

    a) If the odds are the same for both, then I just calculated (1/2)7 based on the 7 remaining choices.

    b) Probability here would be (.7)7 going by the same remaining choices.

    c)For this I did

    (1/2)(1+7)*7/2 which would equal a probability of (1/2)28.

    Was my approach to this problem correct?
  2. jcsd
  3. Apr 9, 2016 #2


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    Science Advisor

    How many bits does the question ask about? Are there any bits it does not ask about?
  4. Apr 9, 2016 #3
    A string of length 10 where the choices are either 0 or 1. The first one is labeled as 1, the last two as 00. This leaves seven choices where the selected bit can be 0 or 1.
  5. Apr 9, 2016 #4


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    Science Advisor

    What part of this problem statement asks about the seven bits in the middle?
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