The population must be normally distributed in order to use the normal model to compute probabilities regarding the sample mean. The sampling distribution of the mean x would be normal with a mean of 69 and standard deviation of 15/√39. The probability that the sample mean x is less than 73.4 is P(z<(73.4-69)/15/√39/√39) = P(z<0.96) = 0.17. The probability that the sample mean x is greater than 70.8 is P(z>1.2) = 0.1155.