Don't you have examples in your class notes and/or textbook?Hello all!

My instructor gave us these questions for practice and I need to be walked through them because I am lost and need to be assisted once again to make sue I know what I am doing. Okay, here they are:

Problem A: To revise an existing inventory system, a company needs to know something about the lead time for orders it places for a critical part. The company looks at the last 20 orders placed and finds that the lead time in days are: 1,4,6,7,4,5,6,8,4,5,7,8,4,6,7,10,4,6,7,11.

a-What is the mean lead time for an order?

Mr F says: Add up the data. Divide the total by how many data there are.

b-What is the median lead time for an order?

Mr F says: Order the data from smallest to biggest:

1, 4, 4, 4, 4, 4, 5, 5, 6, 6, 6, 6, 7, ,7 ,7 ,7 8, 8, 10, 11.

Find the middle:

1, 4, 4, 4, 4, 4, 5, 5, 6, 6, | 6, 6, 7, ,7 ,7 ,7, 8, 8, 10, 11.

The median is 6.

c-What is the mode lead time for an order?

Mr F says: Apply the definition of the mode.

d-What statistic or statistics do you think represents a typical lead time and why?

Mr F says: Choose between mean, median and mode. Which one best represents a typical datum? Why?

Prob. B A normal population has a mean of 20.0 and a standard deviation of 4.0.

a-Compute the z-value associated with 25.

b-Compute the z-value associated with 18.

Mr F says: In both cases apply the usual formula , where is the mean and is the standard deviation:

a. .

Thanks for all your help!!