Problem 8.2. Oleg bought a chocolate bar for $n$ rubles, and after some time, he sold it for 96 rubles. It turned out that he sold the chocolate bar for exactly $n \%$ more than he bought it for. For how many rubles did Oleg buy the chocolate bar?
Answer: 60.

Solution. From the condition of the problem, it follows that $96=n \cdot\left(1+\frac{n}{100}\right)$. Transforming this equation, we get

$$
0=n^{2}+100 n-9600 \quad \Leftrightarrow \quad 0=(n+160)(n-60)
$$

Thus, $n=60$, since the chocolate bar cannot cost a negative number of rubles.