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

[samanthaX]

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

 

[tkhunny]

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.