An SRS of 20 orangutans is selected, and 65 cc of blood is to be drawn from each orangutan using a 100 cc syringe. In the sample, the mean volume is 64 cc and the standard deviation is 12 cc. Assume that in the population of all such procedures, the amount of blood drawn follows a Normal distribution with mean μ.
Reference: Ref 17-1

A 90% confidence interval for the population mean volume based on these data is
A. 64 ± 2.68.
B. 64 ± 4.64.
C. 64 ± 5.62.
D. 64 ± 6.84.

Question

An SRS of 20 orangutans is selected, and 65 cc of blood is to be drawn from each orangutan using a 100 cc syringe. In the sample, the mean volume is 64 cc and the standard deviation is 12 cc. Assume that in the population of all such procedures, the amount of blood drawn follows a Normal distribution with mean μ.
Reference: Ref 17-1

A 90% confidence interval for the population mean volume based on these data is
A.	64 ± 2.68.
B.	64 ± 4.64.
C.	64 ± 5.62.
D.	64 ± 6.84.

anonymous · Answer

i got the answer 64+/- 4.414. what am i doing wrong?

valpey · Answer

Well, maybe there is some funny play with Sample Standard Deviation here, but I think you are again looking at a question with weird multiple choice options. 64 plus or minus 4.414 is right unless you are meant to infer sample standard deviation from an incorrectly calculated "population standard deviation" of 12cc which would correct to 12.31cc and instead give a 90% CI with 64 plus or minus 4.53; also not in your answer options.

valpey · Answer

I pretty much doubt that, but if you want to talk about Sample Standard Deviation, we can. I just don't think it is part of the discrepancy.

anonymous · Answer

yeah its tricky!

anonymous · Answer

one more question -- i have 10 min left!