1. Body Mass Index (BMI) is a number calculated from a person's weight and height and is calculated by the formula: weight (kg) / [height (m)]². Though somewhat controversial and not meant to be used as a diagnostic criteria, it can be used to characterize body type and (with caution) fitness and health using readily available data. Commonly accepted classifications are listed below:

Below 18.5 is underweight;

18.5 to 25 is normal;

25 to 30 is overweight;

Above 30 is obese.

Based on a study, the BMI for middle-aged US males has a normal distribution with a mean of 27 and a standard deviation of 4.5. What is the probability that the average BMI is considered underweight based on BMI criteria for a randomly selected sample including 40 middle-aged US males?