In: Statistics and Probability
According to a recent report, a sample of 360 one-year-old baby boys in the United States had a mean weight of 25.5 pounds. Assume the population standard deviation is =σ5.1 pounds.Construct a 99.5% confidence interval for the mean weight of all one-year-old baby boys in the United States. Round the answer to at least one decimal place.
We are given that n=360 and 25.5 pounds, 5.1. We need to find out the 99.5%. Since the sample size is large and is known, we shall use the normal distribution Z value to calculate the confidence interval. Here (Since 1-0.005 = 0.995).
The formula to calculate the confidence interval is:
From the tables or from Excel, the value of can be found as 2.807. (In Excel, we need to use the function, NORM.S.INV(0.0025. Substituting the values, we get
Confidence interval =
The 99.5% confidence interval rounded to one decimal place is .
The lower limit is 24.7 pounds and the upper limit is 26.3 pounds.