Confidence Intervals

Question

You intend to estimate a population mean with a confidence interval. You believe the population to have a normal distribution. Your sample size is 29.

Find the critical value that corresponds to a confidence level of 80%.

(Report answer accurate to three decimal places with appropriate rounding.)

Answer 1

We are going to use the t-value corresponding to an 80% CI (upper tail probability of 0.1) with 29-1 = 28 degrees of freedom = 1.313. On TI 83/84 calculator enter invT(0.9,28).