The 2012 U.S. Pet Ownership and Demographics Sourcebook reported that 36.5% of American households have a pet dog and 30.4% have a pet cat. 

a. Does it follow from this information that 36.5% + 30.4% = 66.9% of American households have a pet dog or a pet cat? Explain your answer, referring to at least one probability rule. 

b. Based on the given percentages, what is the smallest possible value for the percentage of American households that have a pet dog or a pet cat?

c. Describe (in words) the (very unrealistic) circumstance in which this (your answer to part (b)) would occur.