Question

Sales personnel for Skillings Distributors submit weekly reports listing the customer contacts made during the week. A sample of 85 weekly reports showed a sample mean of 18.5 customer contacts per week. The sample standard deviation was 5.6. Provide 90% and 95% confidence intervals for the population mean number of weekly customer contacts for the sales personnel.

90% Confidence interval, to 2 decimals:

( ,  )

95% Confidence interval, to 2 decimals:

What is the 95% confidence interval for the population mean (to 1 decimal)?

Answer 1

(A) alpha = 1 - confidence level = 1-0.90 = 0.10

sample size n = 85, so degree of freedom= n-1= 85-1 = 84

t critical = T.INV.2T(alpha,n-1) = T.INV.2T(0.10,84) = 1.663

sample mean xbar = 18.5 and standard deviation s = 5.6

(B) alpha = 1 - confidence level = 1-0.95 = 0.05

sample size n = 85, so degree of freedom= n-1= 85-1 = 84

t critical = T.INV.2T(alpha,n-1) = T.INV.2T(0.05,84) = 1.989

sample mean xbar = 18.5 and standard deviation s = 5.6