Body mass is a simple index of weight for height that is commonly used to classify overweight and obesity in adults. According to a study by the National Center for Health Statistics, the BMI of American men is normally distributed with a mean of 26.6 kg/m and a standard deviation is 5.2kg/m. If 100 different American men are randomly selected, what is the probability that their mean BMI is less than 25.0 kg/m ( the cutoff between normal and overweight)?