I just don't understand it

Question

The effectiveness of a blood-pressure drug is being investigated. An experimenter finds that, on average, the reduction in systolic blood pressure is 75.9 for a sample of size 701 and standard deviation 13.1.

Estimate how much the drug will lower a typical patient's systolic blood pressure (using a 80% confidence level).

Enter your answer as a tri-linear inequality accurate to one decimal place (because the sample statistics are reported accurate to one decimal place).

____ < µ < ____

Answer 1

You are to find an 80% confidence interval for the population mean, given that the sample size (n) is 701, the sample mean is 75.9 and the sample standard deviation is 13.1.

The formula for an 80% confidence interval is:

mean +/- t-critical * sample SD/square root (n)

t-critical is the value from the t-distribution table for 10% upper tail and 700 degrees of freedom, which is approximately 1.29 (if 700 DOF is not in table, use value for next lowest DOF).

You now have the values to plug into your formula and get your CI.