1. If x is a binomial random variable where n = 100 and p = 0.3, find the probability that x is less than or equal to 20 using the normal approximation to the binomial. Show work and excel functions if possible.
If X ~ binomial (n,p) where n > 20 and 0.05 < p < 0.95 then approximately X has the Normal distribution with mean E(X) = np and standard deviation
so is approximately N(0,1).
In this context, we have
n= 100
p = 0.3
E(X) = n*p = 100*0.3 = 30
The probability that x is less than or equal to 20 using the normal approximation to the binomial.
So, the probability that x is less than or equal to 20 is 0.0146
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