The question is incomplete. The complete question is :
The National Center for Health Statistics reports that 25% of all Americans between the ages of 65 and 74 have a chronic heart condition. Suppose you live in a state where the environment is conducive to good health and low stress and you believe the conditions in your state promote healthy hearts. To investigate this theory, you conduct a random telephone survey of 25 persons 65 to 74 years of age in your state.
Suppose only one person in your survey has a chronic heart condition. What is the probability of getting one or fewer people with a chronic heart condition in a sample of 25 if 25% of the population in this age bracket has this health problem?
Solution :
Chronic heart disease is a condition where a person's heart have trouble to pump blood to the body. It develops over a period of time.
In the context, we can see from the figures from National Center for Health Statistics that the expected number of persons of age 65 - 74 years having a chronic heart disease is about
25 % of 25 = 6.25
Now by Poisson's ratio, the probability of choosing the sample where only one person having heart disease is 1.4%