Business arithmetic developed because of the need of economy for a faster and simpler solution of practical assignments. Problems in economy are solved by using general rules and schemas, hence the application of percentage and per mille, ratio, proportion and chain calculation. The purpose of this paper is to show, on concrete examples, the application of business arithmetic. Percentage (per mille) indicates the unit taken from one hundred (thousand) units of some quantity. In most economic calculations, rule of three is used: from the three known quantities the fourth unknown is being calculated. Average is used to determine the average value from multiple quantities. Continued ratio is used to divide a quantity into more parts according to specific criteria, whereas the compound proportion gives the answer how to mix quantities of certain intensity in order to get an average intensity mixture. Chain calculation is schematic process that finds the relationship between quantities given by directly proportional quantities. Chain calculation is mostly used for conversion of currencies, where it finds relationship between dissimilar currencies.