The population of Philip’s hometown is on the rise. One way of expressing the population each year is by taking the previous year’s population and considering the changes based on all citizens who have left and all who have newly arrived.

If Pn represents the new population, Po the old population, N the newly arrived citizens and L the citizens who have left, give an equation that combines these together in a way that will correctly calculate the new population.

Express the new population only in terms of a sum of these terms and not a difference of the terms. i.e. write your answer in the format : Pn=a+b+(-c)