jan_ai
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All students in a particular school study math, for which the failure rate is 20%. Assuming
that the number of students who fail math follows a binomial distribution, for a class
of nine students, calculate
(i) the variance for the number of persons who failed math in the class
[2 marks]
(ii) the probability that exactly two students failed math
[2 marks]
(iii) the probability that at least three students failed math.
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vc94
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(i) Here X~B(9, 0.2) The variance formula is np(1-p)
(ii) P(X=2) can do on a calculator or use formula nCr(p^r)(1-p)^(n-r)
(iii) P(X>=3) = 1 - P(X<=2) since X is discrete variable.
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