Suppose a measurement is made on some physical characteristic whose value is known, and let X denote the resulting measurement error. For an unbiased measuring instrument or technique, the mean value of X is 0. Assume that any particular measurement error is normally distributed with variance s2 . Let X1,... Xn be a random sample of measurement errors. a. Obtain the method of moments estimator of s2 . b. Obtain the maximum likelihood estimator of s2 .