You may need to use the appropriate appendix table or technology to answer this question. Sales personnel for Skillings Distributors submit weekly reports listing the customer contacts made during the week. A sample of 67 weekly reports showed a sample mean of 18.5 customer contacts per week. The sample standard deviation was 4.2. Provide a 90% confidence interval for the population mean number of weekly customer contacts for the sales personnel. Provide 95% confidence interval for the population mean number of weekly customer contacts for the sales personnel. Step 1 Since a sample standard deviation is given, the t distribution will be used to construct the specified confidence intervals. Recall the structure of a confidence interval given below where x is with n - 1 degrees of freedom, s is the sample standard deviation, and n is the sample size. the sample mean, ta/2 is the value of t that corresponds to an upper tail area of 2 S The value of alpha is found by setting the confidence level equal to (1 - a) and solving for a. To solve for a, first convert 90% to a probability, also representative of an area, so that the t table may be used. probability= percentage 100% % 100%