# statistics

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#1
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 maths in the class
[2 marks]
(ii) the probability that exactly two students failed maths
he probability that at least three students failed maths
0
1 month ago
#2
Most of this should be textbook
i. variance = np(1-p)

ii. P(X=2) using (n r)(p^r)(1-p)^(n-r)

iii. P(x=>3) = 1- P(x<3) using the binomial distribution (or you can san 1 - P(X=<2)).

Personally I can't understand why the failure rate of a math test would follow a binomial distribution, but there you go.
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