Problem 2. In class 4-b, there were 24 students. Each student can choose whether to study the subjects of informatics and German. 15 students study informatics, 12 study German, and 8 students do not study either informatics or German. How many students from class 4-b study both informatics and German at the same time?
Solution. Out of 24 students in the class, 8 do not study either informatics or German. This means $24-8=16$ students have chosen at least one of the subjects. Since 15 study informatics and 12 study German, which totals $15+12=27$, we get that $27-16=11$ students study both subjects.