13. (3 points) A cold drink shop launched a "Buy one get the second at half price" promotion. Xiaogang bought 2 cups of drinks and spent a total of 13 yuan 5 jiao. What is the original price of one cup of drink? $\qquad$ yuan.
【Analysis】Regarding the original price of the first drink as unit "1", the price of the second drink is $\frac{1}{2}$ of the first drink. According to the problem: the price of the first drink $\left(1+\frac{1}{2}\right)$ is 13.5 yuan. Based on the known fraction of a number, to find the number, use division.

【Solution】Solution: $13.5 \div\left(1+\frac{1}{2}\right)$,
$$
\begin{array}{l}
=13.5 \div 1.5, \\
=9 \text { (yuan); }
\end{array}
$$

Answer: The original price of one drink is 9 yuan;
Therefore, the answer is: 9.

