The weights of ice cream cartons are normally distributed with a mean weight of 12 ounces and a standard deviation of 0.5 ounce (a) What is the probability that a randomly selected carton has a weight greater than 12.31 ounces? (b) A sample of 16 cartons is randomly selected. What is the probability that their mean weight is greater than 12.31 ounces? (a) The probability is (Round to four decimal places as needed.)