The following relative frequency distribution describes the household incomes for families living in a suburban community:
Income Relative Frequency
Less than $20,000........ 0.10
$20,000–under $40,000..... 0.20
$40,000–under $60,000..... 0.30
$60,000–under $80,000..... 0.25
$80,000 or more........ 0.15
a. For a randomly selected household, what is the probability that its annual income is less than $80,000?
b. If a household is known to have an income of at least $20,000, what is the probability that its annual income is in the $60,000–under $80,000 category?
c. Two households are randomly selected from those whose income is at least $40,000 per year. What is the probability that both of these households are in the $80,000 or more category?