At a school Science Fair, it was observed that half of the elementary school students and a quarter of the high school students present at this event bought one sticker each.

| SCIENCE FAIR |  |
| :---: | :---: |
| Price of Stickers (unit) |  |
| $\mathrm{R} \$ 0.30$ | elementary school students |
| $\mathrm{R} \$ 0.50$ | high school students |

It was also noted that the number of high school students present who did not buy stickers was twice the number of elementary school students who did not buy stickers. Knowing that $\mathrm{R} \$ 38.00$ was raised from the sale of stickers to students from these two levels, how many students from each level participated in the fair?
Let $x$ and $y$ be the number of elementary and high school students respectively, present at the fair. Thus, the number of those who bought a sticker is:

$$
\frac{x}{2} \text { from elementary school and } \quad \frac{y}{4} \text { from high school; }
$$

and those who did not buy stickers were

$$
\frac{x}{2} \text { from elementary school and } \frac{3 y}{4} \text { from high school. }
$$

Among the students who did not buy stickers, those from high school represent double the number of those from elementary school. Therefore,

$$
\frac{3 y}{4}=2 \times \frac{x}{2} \Rightarrow \frac{x}{2}=\frac{3 y}{8}
$$

Knowing that the total amount collected was $R \$ 38.00$, we conclude that:

$$
\begin{aligned}
38=0.30 \frac{x}{2}+0.50 \frac{y}{4}=0.30 \frac{3 y}{8}+0.50 \frac{y}{4} & \Rightarrow 1.90 y=8 \times 38 \\
& \Rightarrow y=160
\end{aligned}
$$

Now, from $x=\frac{3 y}{4}$, it follows that $x=120$.