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Answer:
The sample size needed if the margin of error of the confidence interval is to be about 0.04 is 18.
Step-by-step explanation:
In a sample with a number n of people surveyed with a probability of a success of , and a confidence level of
, we have the following confidence interval of proportions.
In which
z is the zscore that has a pvalue of .
The margin of error is:
95% confidence level
So , z is the value of Z that has a pvalue of
, so
.
Past studies suggest this proportion will be about 0.15
This means that
Find the sample size needed if the margin of error of the confidence interval is to be about 0.04
This is n when M = 0.04. So
Rounding up
The sample size needed if the margin of error of the confidence interval is to be about 0.04 is 18.