My professor sent us a homework question that had me puzzled. The homework consisted of four questions that were related and fifth one that is totally independent of the first four. The first four dealt with High School test scores so none of their data is applicable to the fifth. This is the fifth question.
"5. How large must the sample size be for 95% CI to lie w/in ± 4 mg/100ml of the population mean, μ.
To answer the last question, note the following:
Xbar= μ ± m (margin or error) where m = Z σSDOM = Z (S^ / √N) Therefore
N = Z^2(S^)2/m2 "
I have Z = 1.96 and m =8. I think it is eight because plus or minus 4 totals up to 8. I could be wrong about that part. I have no idea where to get S hat (SD for the population). He did not include any X values or a mean with the homework assignment. I am completely stumped. After several hours of research I found a very crude approximation for the SD. It is SD = Range/4. He did not mention this in class so I am hesitant to use it. I see no way to solve this without the SD or at least some approximation. As mentioned before, the only information I was given is quoted above.
