A confidence interval has two bounds, a lower bound and an upper bound.
A confidence interval is symmetric, which means that the point estimate used is the mid point between these two bounds, that is, the mean of the two bounds.
The margin of error is the difference between the two bounds, divided by 2.
a. What is the point estimate of the mean salary for all college graduates in this town?
Mean of the bounds, so:
(38737+50463)/2 = 44600.
The point estimate was of $44,600.
b. Determine the sample size used for the analysis.
First we need to find the margin of error, so:
Relating the margin of error with the sample size:
We have that to find our level, that is the subtraction of 1 by the confidence interval divided by 2. So:
Now, we have to find z in the Z-table as such z has a p-value of .
That is z with a pvalue of , so Z = 1.64.
Now, find the margin of error M as such
In which is the standard deviation of the population and n is the size of the sample.
