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 28.8 milligrams and standard deviation of 2.1 milligrams for a sample of cigarettes. Construct a 90% confidence interval for the mean nicotine content of this brand of cigarette.

Question

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 28.8 milligrams and standard deviation of 2.1 milligrams for a sample of  cigarettes. Construct a 90% confidence interval for the mean nicotine content of this brand of cigarette.
Choose one answer.   A. 28.8 ± 1.361   
  B. 28.8 ± 1.381   
  C. 28.8 ± 1.283   
  D. 28.8 ± 1.302

PsyDAG · Answer

Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the Z value for the smaller portion = .05. (90% confidence interval leaves 5% at each end.)

Mean ± 1.645(SD) = ?

However, this does not match any of the answers given. Do you have any typos?

jc · Answer

no, you have to use a t value. you did the problem wrong.