Suppose the weights of college textbooks are normally distributed with a population mean of 4 pounds and a population standard deviation of 1.2 pounds. Suppose randomly sample and weigh 16 textbooks. Answer the following questions:
a) What is the probability that the sample average of the 16 textbooks is less than 3.5 pounds? (use 2 decimal places in your answer))
b) Imagine the distribution of all possible samples averages of textbook weights (with ). What is the weight that separates the lightest 25% of sample averages from the heaviest 75% of sample averages? (round your answer to the nearest tenth of a pound)