A researcher collected data from a sample of correctional officers and found that on average they made 47,173 dollars a year with S=6,364. (10 points) a. Calculate the z-score for a correctional officer who makes 40,000 dollars a year b. Calculate the z-score for a correctional officer who makes 50,000 dollars a year? c. What proportion of correctional officers make more than 40,000 dollars a years?

a)

b)

c)

And we can find this probability using the complement rule and the normal standard distribution or excel and we got:

Step-by-step explanation:

Previous concepts

Normal distribution, is a "probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean".

The Z-score is "a numerical measurement used in statistics of a value's relationship to the mean (average) of a group of values, measured in terms of standard deviations from the mean".  

Part a

Let X the random variable that represent the amount of money of a population of interet, and we know the following info:  

Where and

We can assume that the sample size is large and the estimators can be used as a good description for the parameters  

The z score for 40000 would be:

Part b

The z score for 50000 would be:

Part c

We are interested on this probability

And the best way to solve this problem is using the normal standard distribution and the z score given by:

If we apply this formula to our probability we got this:

And we can find this probability using the complement rule and the normal standard distribution or excel and we got:

the answer is d

step-by-step explanation: