B3. At the Pythagoras Lyceum, all classes have a maximum of 25 students. In one of the classes, a survey is conducted about all sorts of things, and everyone fills out all the questions. In this class, it turns out that $31 \%$ of the students have a black bicycle and that $94 \%$ of the students live more than $1 \mathrm{~km}$ away from school. These percentages are rounded to the nearest whole number. How many students are there in that class?
B3. 16 Let the number of students in the class be $n$. Since there are at most 25 students in the class, each student is at least $4 \%$ of the total. The $94 \%$ of students who live more than 1 $\mathrm{km}$ from school must be $n-1$ students: indeed, it cannot be all $n$ students, and $n-2$ students can account for at most $92 \%$ of the total. Therefore, one student is approximately $6 \%$ of the class.

One student thus corresponds to a percentage between 5.5 and 6.5. This means that $31 \%$ corresponds to 5 students, because 4 students account for at most $4 \cdot 6.5 = 26$ percent, and 6 students account for at least $6 \cdot 5.5 = 33$ percent.

Five students thus correspond to a percentage between 30.5 and 31.5. This means that 15 students account for at most $\frac{15}{5} \cdot 31.5 = 94.5$ percent. The number of students must therefore be 16.