Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability (± .025) and its Z score = 1.96
95% = mean ± 1.96 SEm
SEm = SD/√n
To help consumers assess the risks they are taking, the Food and Drug Administration (FDA) publishes the amount of nicotine found in all commercial brands of cigarettes. A new cigarette has recently been marketed. The FDA tests on this cigarette yielded mean nicotine content of 27.3 milligrams and standard deviation of 2.1 milligrams for a sample of cigarettes. Construct a 95% confidence interval for the mean nicotine content of this brand of cigarette.
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