An influenza epidemic spreads at a
rate proportional to the product of the number of people in-
fected and the number not yet infected. Assume that 100 people
are infected at the beginning of the epidemic in a community of
20,000 people, and 400 are infected 10 days later.
a. Write an equation for the number of people infected, y, af-
ter t days.
b. When will half the community be infected?
