Suppose that n = 100 random samples of water from a freshwater lake were taken and the calcium concentration (milligrams per liter) measured. A 95% CI on the mean calcium concentration is 0.49 0.82. a) What is the value of the sample mean? b) What is the value of the standard error? (hint: assume the population standard deviation is known) c) Would a 99% CI calculated from the same sample data be longer or