A problem of my statistics class....?

Question

Let's say we want to do a survey of 80 people. What is the probability that at least 30 of them are men?

Can I actually do something with this information? What do I need to use ? How do I do it?

Answer 1

This would be a binomial. Assuming that p=1/2 , equal probability of male or female.

Then it's like 80 trials with success (male) or failure (female)

At least 30 male means that you have to add probs of 30, 31, 32, ...,80. It's easier to add probs of 1,2,...,29 and subtract from 1.

80 is a large enough number to use the normal approximation.

For the normal, the mean would be 80/2 = 40. So, at least 30 is

1-P(X
convert X to Z to use standard tables.