Hi
On Mon, 27 Sep 1999, Susan Shapiro wrote:
> If you know the mean and standard deviation for a population for the weight
> of one item and you are trying to estimate the probability of a range of
> weights when 12 items are weighed at the same time, can you simply multiply
> the mean and SD by 12?
The best way to think of this is in terms of the distribution of
_mean_weight_ for 12 (or whatever number) items. From the
Central Limit Theorem, SEmean = SD/sqrt(n), so we can determine
the probability of the sample mean weight falling within various
distances of Mu, the population mean (e.g., +/- 1, 2, ...
SEmean). Once you have figured the desired upper and lower
boundaries for the mean sample weight, multiply those boundaries
by 12 to get the total weights. With some algebra, one could
figure out how to compute the sum boundaries directly. This
exercise is left for the reader!
Best wishes
Jim
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James M. Clark (204) 786-9757
Department of Psychology (204) 774-4134 Fax
University of Winnipeg 4L05D
Winnipeg, Manitoba R3B 2E9 [EMAIL PROTECTED]
CANADA http://www.uwinnipeg.ca/~clark
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