Arithmetic density is the total number of people in an area. This is most useful when looking at a single town or city, where the population is evenly distributed.
It is the population divided by the arable land. This is used to understand how much food the land can provide for a certain amount of people.
It is the amount of farmers divided by the total amount of arable land. You can use this to understand how many farmers are used for the amount of land. If their is a high number, then the farmers use old fashion methods. They are not as technological advanced as other countries with a lower agricultural density.