Suppose that news spreads through a city of fixed size of 50

Suppose that news spreads through a city of fixed size of 500000 people at a time rate proportional to the number of people who have not heard the news. Let y(t) denote the number of people who have heard the news t days after it has happened. If y is the number of people who have heard the news at a certain time, what is the formula for the number of people who have NOT heard the news: number of people who have not heard the news = (the only variable that should appear in your answer is y).

Solution

500000-y because there are 500000 people in the town and y have heard the news