sample size for conf. level of .95, int. of 5, pop. of 20K

With a confidence level of .95 and a confident interval of 5 and a population of 20,000 what is the sample size?

With a confidence level of .99 and a confident interval of 5 and a population of 20,000 what is the sample size?

And finally, using the sample size for question 1 and 2 and a response distribution of 50% (i.e., percentage box) what is the confidence interval for questions 1 and 2.

If you had the time to explain how you figured those 2 questions out, that would help me tremendously :~), I have been trying to figure it out, by reading the book, but to no avail....

Thank you in advance for any assistance you can provide
Sincerely,
Grateful
Samantha

You should have a formula for that.

\(\displaystyle \L\;n\;=\;\frac{z^{2}s^{2}}{d^{2}}\)

n is the sample size

z is the z-score you have to lookup that goes with your level of confidence

s^2 is your best estimate of the Variance of the population. Use 0.5 if there is absolutely NO other information. This will maximize the sample.

d is the desired maximum error.

Fill in the blanks and pop out the answer.