Finite Mathematics

Proof Prove properties 2, 3, and 4 of Theorem 2.6.

Epidemic Model In a population of 200,000 people, 40,000 are infected with a virus. After a person becomes infected and then recovers, the person is immune cannot become infected again. Of the people who are infected, 5 will die each year and the other will recover. Of the people who have never been infected, 25 will become infected each year. How many people will be infected in 4 years?