The probability of an event occur >90% of the time.

[cyclonefb3]

An actor claims he signs 90% of autographs asked for. A sample of 100 fans is taken with a normal distribution. What is the probability that the actor will give more than 90% of them autographs.

mean = 60
SD = 30
n=100

So I did this:

z = estimate - hypothesis 90 - 0
-------------------- --------- = 3
SD of estimate 30


z = 3

When you look on a normal table the z value at 3 = .9987

Does that mean there is 99% probability of this happening or am I doing this wrong?

 

[tkhunny]

You have the wrong side. It appears you have calculated the probability of LESS than 90%.