ten randomly selected people were asked how long they slept at night. The mean time was 7.1 hours and the (sample) standard deviation was 0.78 hours. Find the 95% confidence interval of the mean time. Assume the variable is normally distributed.

Answer 1

95% confidence interval indicates that you have 5% outside the confidence interval and 2.5% on either side. This is an area of .025. You can use a calculator or a t-table to find the critical value.

Multiply that value times the standard deviation.

add this value to the mean and then subtract this value to the mean which will give you the confidence interval. Always write the confidence interval with the smaller value first.