 Howdy. Today, we're going to build a confidence interval for a population mean. You measure 26 textbooks as weights, and you find they have a mean weight of 55 ounces. Assume the population standard deviation is 8 ounces. Based on this, construct a 90% confidence interval for the true population mean of textbook weight. Round to three decimal places. We will use technology for this. So in this example, sigma population standard deviation is known. So we can actually use our standard normal RZ distribution. Out of all the information they gave me, I know that the sample size is 26. I know that the mean weight X bar is 55. And I know that the population standard deviation is going to be 8. My confidence level in this case is 90% or .9. This is what I need to put into Google Sheets. So I will go to Google Sheets and make sure you go to the data list tab. And I will focus my attention down here on the one variable confidence level P value Z distribution. We're using Z because we know sigma. We know the population standard deviation. X bar is 55. Sigma is 8. Sample size is 26. Confidence level in this case is .9 or .90. And this gives me a confidence interval of a lower limit of 52.419 and an upper limit of 57.581. And that's all rounded to three decimal places. So the true population mean for textbook weights is between an upper limit of 57.581 and a lower limit of 52.419. You can also write this in interval notation as well. So the correct interpretation is with 90% confidence. The true population mean of textbook weights is between 52.419 ounces and 57.581 ounces.