In a sample of 500 families, 50 have a yearly income of less than $40,000, 180 have a yearly income of $40,000 to $80,000, and the remaining families have a yearly income of more than $80,000. Write the frequency distribution table for this problem. Calculate the relative frequencies for all classes. Suppose one family is randomly selected from these 500 families. Find the probability that this family has a yearly income of
a. Less than $40,000 

b. More than $80,000