More On Sampling Distributions.....

Okay so I started on this one too....but once again I don't know if my method is correct....

Suppose that the distribution of all male students on your campus is Normal with mean 70 inches and standard deviation 2.8 inches.

(a) If you choose one student at random, what is the probability that he is between 69 and 71 inches tall???

Here's what I have done so far....



z=69-70/2.8= -.35

With table A:

F(z)= .3632

1-.3632= .6368= 64%

Now should I use the equation o/sqrt(n) order to get the new standard deviation or am I doing it the right way.....I know that the problem isn't finished but....I need to know if I am doing it the right way before I finish....

(b). What is the probability that the mean height of your sample is between 69 and 71 inches tall?

I have NO IDEA what they are asking me to do here.....please help me!!!