Question

you want to compute a 95% confidence interval for the mean of a population with unknown population standard deviation. the sample size is 30. the value of t* you would use for this interval is a) 1.645 b) 1.699 c) 1.96 d) 2.045​

Answer 1

Answer: d) 2.045

Use either a table or a calculator to find this value. The t table should be found in the back of your stats textbook (if you dont have a textbook then you can find a free online t table by searching it out). See the attached image below for how I used a table to get the answer.

If you use a calculator, then you'll use the inverse T function. If n > 30, then you would be able to use a Z distribution instead of a T distribution which would mean that z = 1.96 is the critical value used. But instead, n = 30 does not make n > 30 true. Keep in mind that the degrees of freedom (df) are df = n-1 = 30-1 = 29.