Tuesday, December 29, 2015

3.5. A software package consists of 12 programs, five of which must be upgraded. If 4 programs are randomly chosen for testing, (a) What is the probability that at least two of them must be upgraded?(b) What is the expected number of programs, out of the chosen four, that must be upgraded?

3.5. A software package consists of 12 programs, five of which must be upgraded. If 4 programs
are randomly chosen for testing,
(a) What is the probability that at least two of them must be upgraded?
(b) What is the expected number of programs, out of the chosen four, that must be
upgraded?


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  1. (o|O)_whatisitfrom__(O|o)January 1, 2019 at 5:01 AM

    I don't understand why the short solution work. Why are you using sum of Bernoulli?
    From a book I see `any Binomial variable X can be represented as a sum of independent Bernoulli variables`
    Here X1 directly affect on probability of X2,X4
    If X1 = 1, P{X2} is 4/11
    X2 = 0, P{X2} is 5/11
    Does the Xi remain independent?

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