You work for a soft-drink company in the quality control division.  You are interested in the standard deviation of one of your production lines as a measure of consistency. The product is intended to have a mean of 12 ounces, and your team would like the standard deviation to be as low as possible.  You gather a random sample of 18 containers.  Estimate the population standard deviation at a 95% level of confidence. 11.97 12.04 12.03 12.01 12.09 11.84 11.92 12.01 11.89 11.95 12.01 11.74 11.77 12.09 12 12.18 11.96 12.06   Note: Keep as many decimals as  possible while making these calculations. If possible, keep all answers exact by storing answers as variables on your calculator or computer. a)  Find the sample standard deviation:   b)  Find the lower and upper χ2χ2  critical values at 95% confidence: Lower:     Upper:  c)  Report your confidence interval for σ:  (     ,      )

Definition Definition Measure of central tendency that is the average of a given data set. The mean value is evaluated as the quotient of the sum of all observations by the sample size. The mean, in contrast to a median, is affected by extreme values. Very large or very small values can distract the mean from the center of the data. Arithmetic mean: The most common type of mean is the arithmetic mean. It is evaluated using the formula: μ = 1 N ∑ i = 1 N x i Other types of means are the geometric mean, logarithmic mean, and harmonic mean. Geometric mean: The nth root of the product of n observations from a data set is defined as the geometric mean of the set: G = x 1 x 2 ... x n n Logarithmic mean: The difference of the natural logarithms of the two numbers, divided by the difference between the numbers is the logarithmic mean of the two numbers. The logarithmic mean is used particularly in heat transfer and mass transfer. ln x 2 − ln x 1 x 2 − x 1 Harmonic mean: The inverse of the arithmetic mean of the inverses of all the numbers in a data set is the harmonic mean of the data. 1 1 x 1 + 1 x 2 + ...