Percentages are one of the mathematical concepts that we encounter in everyday life. People face daily life situations related to the price and percentage of goods and services. In order for them not to suffer financial losses, the school must be well versed in the problems of prices and percentages found in mathematics. Methodical approaches to solving "about price" problems found in the school course are not shown schematically, which causes difficulties in solving complex problems by students. Therefore, the development of functional mathematical and financial literacy of many students within the framework of this topic is not at the desired level. The article discusses effective approaches to solving problems of calculating the percentage change in the price of goods in the school mathematics course as an urgent problem of the development of functional mathematical and financial literacy of students. Students are presented with examples of tasks for applying mathematical knowledge and skills in real life, as well as test papers and assessment criteria.