Arandom sample of 25 fields of rye has a mean yield of 31.2 bushels per acre and standard deviation of 6.99 bushels per acre. determine the 80% confidence interval for the true mean yield. assume the population is approximately normal. (a) find the critical value that should be used in constructing the confidence interval. round your answer to three decimal places. (b) construct the 80% confidence interval. round your answer to one decimal place.