Statistics and Probability question

Use the given information to find the number of degrees of freedom, the critical values x, and Xp , and the confidence interval estimate of o. It is reasonable to assume that a simple random sample has been selected from a population with a normal distribution. Nicotine in menthol cigarettes 90% confidence; n =21, s =0.24 mg. Click the icon to view the table of Chi-Square critical values. df = (Type a whole number.)