Espa In an effort to counteract student cheating, the professor of a large class created four versions of a midterm exam, distributing the four versions among the 292 students in the class, so that each version was given to 73 students. After the exam, the professor computed the following information about the scores (the exam was worth 200 points): Group Sample Sample Sample size mean variance Version A 73 156.4 401.3 Version B 73 159.8 316.9 Version C 73 153.4 286.6 Version D 73 151.3 327.3 Send data to calculator Send data to Excel The professor is willing to assume that the populations of scores from which the above samples were drawn are approximately normally distributed and that each has the same mean and the same variance. Answer the following, carrying your intermediate computations to at least three decimal places and rounding your responses to at least one decimal place. (a) Give an estimate of this common population variance based on the variance of the sample means given. (b) Give an estimate of this common population variance by pooling the sample variances given. X