Think of " ∩ " as having a horizontal line drawn throught it like this: "∩", making it look like the letter " A " for the word " AND ". It would be good if we could make the " U " look like an " O " for the word " OR __(OR BOTH) ", but I can't figure out how to do that. But just remember that " ∩ " means " AND ", " U " means " OR __(OR BOTH) ", " ¯ ¯ " means " NOT ", " - " means " BUT NOT ". (a) ¯C¯ = An American who is NOT a smoker (b) ¯C¯ ∩ ¯D¯ = An American who is NOT a smoker BUT NOT having a health problem (c) C ∩ D = An American who is a smoker AND has a health problem (d) D - C = An American who has a health problem BUT NOT a smoker (e) D U C = An American who has a health problem OR is a smoker (OR BOTH) Edwin