Answer:
, rounded up, if needed, citizens should be included in the sample, in which 
is the standard deviation of the population.
Step-by-step explanation:
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 Ztable as such z has a pvalue of 
.
That is z with a pvalue of 
, so Z = 2.056.
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.
Within 4 years of the actual mean
We have to find n for which M = 4. So
, rounded up, if needed, citizens should be included in the sample, in which is the standard deviation of the population.
