statistics hw help !!!

[sarahm]

A study has shown that the interpupillary distance for all adult males is normally distributed with a mean of 65 mm and a standard deviation of 5 mm.

a)What is the probability that the interpupillary distance for a randomly selected male will be between 64 and 67 mm?

b)What is the probability that the mean interpupillary distance for a simple random sample of 25 males will be between 64 and 67 mm? What is the standard deviation of the sample mean here?

alright, so i got the answer for part a by using the z-score, that was easy. But the 'sample of 25 males' part in part b is confusing me. do I use the z-score to figure out part b too? where do i plug the '25' into?? thanks !

 

[galactus]

The sample standard deviation can be found by using

\(\displaystyle \frac{\sigma}{\sqrt{n}}\)

Which is the population SD divided by the square root of the number sampled.

So, the sample SD is 5/5=1

Then, use that in the z formula.