A sixth of the students in a class wear glasses. Among those who wear glasses, a third are girls; in addition, four boys wear glasses. How many students are there in this class?
Our problem here is to find the number of students in the class. As $1 / 6$ of the students wear glasses and, of those, $1 / 3$ are girls, we have that $\frac{1}{3} \times \frac{1}{6}=\frac{1}{18}$ of the students are girls who wear glasses. Since

![](https://cdn.mathpix.com/cropped/2024_05_01_666a1aec7e447b0a6cbeg-042.jpg?height=117&width=1442&top_left_y=861&top_left_x=387)

and $\frac{1}{6}-\frac{1}{18}=\frac{3}{18}-\frac{1}{18}=\frac{2}{18}=\frac{1}{9}$, we conclude that $\frac{1}{9}$ of the class consists of boys who wear glasses, who are in a number of 4. Therefore, $\frac{1}{9}$ of the class corresponds to 4 students $\frac{9}{9}$ of the class corresponds to $4 \times 9=36$ students.

Thus, the number of students in the class is 36.