Suppose that upper x has a discrete uniform distribution f left-parenthesis x right-parenthesis equals startlayout left-brace1st row 1st column 1 divided by 3, 2nd column x equals 1,2,3 2nd row 1st column 0, 2nd column otherwise endlayout a random sample of n equals 39 is selected from this population. find the probability that the sample mean is greater than 2.1 but less than 2.6. express the final answer to four decimal places (e. g. 0.9876).