In a fun mathematics challenge, Natália and her friends are faced with the task of trading stickers of varying sizes: small, medium, and large. They have agreed on specific trading rules, which allow them to exchange different quantities of stickers for others. The rules state that 7 small stickers can be traded for 4 medium stickers, or 5 medium stickers can be traded for 2 large stickers. With her current collection, Natália hopes to optimize her trades to secure the maximum possible number of large stickers.

Currently, Natália possesses a total of 21 small stickers, 13 medium stickers, and only 3 large stickers. By applying the trading rules effectively, she analyzes how to best utilize her stickers to obtain as many large stickers as possible. The solution to this problem reveals that through a series of trades, the maximum number of large stickers Natália can end up with is 13. This emphasizes both the strategic planning involved in mathematical problems and the importance of understanding ratios and proportions in making effective trades.

This mathematics puzzle not only illustrates a practical application of basic arithmetic skills but also highlights the allure of sticker trading among young people. It is featured on the portal of the Brazilian Public School Mathematics Olympiad (Obmep), showcasing initiatives like these that encourage problem-solving and logical reasoning in students across Brazil. Participating in such challenges can further stimulate interest in mathematics and enhance critical thinking abilities among participants.