1. At the end of the school year $u$ in a sixth grade, the conduct grades were distributed as follows: $50 \%$ of the students had good conduct, $\frac{1}{5}$ of the students had poor conduct, and the remaining 9 students had exemplary conduct. How many students were in this sixth grade?
First method:

Let $x$ be the number of students in that sixth grade.

Then the number of students who have a grade of "good" or "poor" in conduct is:

$$
\begin{aligned}
& \frac{50}{100} \cdot x + \frac{1}{5} x = \\
& = \frac{1}{2} x + \frac{1}{5} x \\
& = \frac{5}{10} x + \frac{2}{10} x \\
& = \frac{7}{10} x
\end{aligned}
$$

The remainder, i.e., $\frac{3}{10}$ of the class, consists of students with a grade of "excellent conduct."

Since there are a total of 9 such students, we can write $\frac{3}{10} x = 9$.

Solving the equation gives $x = 30$.