Historically, a certain region has experienced 65 thunder days annually: (A "thunder day" is day on which at least one instance of thunder is audible to a normal human eas Over the past eleven years, the sample mean number of thunder days is 55 with a sample standard deviation of 20. Can you conclude that the mean number of thunder day is less than 652 Use the a = 0.01 level of significance and assume the population is approximately normal with unknoun standard deviation.