Oziel, Thank you so much for taking the time to work through this problem and share. I was having some difficulty with this one specifically. Giving the reason for the answer really helped me to work through the problem. The number of new cases within a certain period divided by the total number of people in the population at risk at the start of the research period is the cumulative incidence of a disease. In this instance, the question asks for the total number of delegates and non-delegates as well as the number of new cases of Legionnaires' disease among delegates and non-delegates