6. Confidence Interval for Standard Deviation (10 pts.) Shown are the ages (in years) of the Presidents at the time of their deaths. 67 90 83 85 73 80 78 79 68 71 53 65 74 64 77 56 66 63 70 49 57 71 67 71 58 60 72 67 57 60 90 63 88 78 46 64 81 93 a. Do the data represent a population or a sample? b. Select a random sample of 12 ages and find the variance and standard c. Find the 95% confidence interval of the standard deviation. d. Find the standard deviation of all the data values. e. Does the confidence interval calculated in question c contain the mea f. If it does not, give a reason why. What assumption(s) must be considered for constructing the confide