The document discusses smoking-related deaths in the United States each year, including 123,800 from lung cancer out of a total of 438,000 smoking-related deaths. It then defines conditional probability as the probability of one event occurring given that another event has already occurred. Using this definition, it calculates the conditional probability that a smoking-related death will be caused by lung cancer as 28%, based on the number of lung cancer deaths divided by the total number of smoking-related deaths.