of nine students, calculate
(i) the variance for the number of persons who failed maths in the class
(ii) the probability that exactly two students failed maths
he probability that at least three students failed maths
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.