Suppose 60% of adults have a college degree. If I take a random sample of 80 adults, what is the probability at least 50% of them have a college degree?

Answer 1

Use the normal approximation to the binomial distribution.

mean = np = 80 * .6 = ?

standard deviation = √npq = √(80 * .6 * .4) = ?

Calculate. (Note: q = 1 - p)

Next use z-scores:

z = (x - mean)/sd

x = 80 * .5 = ?

Once you have the z-score, find the probability using the z-table.

I hope this will help get you started.