can someone please please help me with these, I have no idea how to do these practice problems, thank u?

Question

Suppose that monthly sales volume for a product is normally distributed, with a mean of 500 units and a standard deviation of 50 units. If x denotes the number of units sold in a month, what are the following probabilities:

P(x < 450)
P(x > 600)
P(400 < x < 450)

Answer 1

First find the z score using the formula z = (number - mean)/s.d.

For the 450, z = (450 - 500)/50 = -1.

You can either apply the 68-95-99.7% rule or look at your z score table. If you use the table, find the z score and read the decimal from the table. That will be your probability.

For the 600, find the z score. You can then do the same thing as for the 450.

For your third problem, find the two z scores, look up the decimals in the z score table, and subtract.

Answer 2

How many standard deviations are each of these?

P(x < 450) is one sd below the mean.

P(x > 600) is two sd above the mean.

P(400 < x < 450) is from two sd below the mean to one sd below the mean.

Get out your normal distribution and look up the first two. To do the third, look up the probability of each and subtract.

Answer 3

I'm 61 years old, too old to be going back to school!!