8. (10 points) Every day, Xiaoming has to pass through a flat section $AB$, an uphill section $BC$, and a downhill section $CD$ (as shown in the figure). It is known that $AB: BC: CD=1: 2: 1$, and Xiaoming's speed ratio on the flat section, uphill section, and downhill section is 3: 2: 4. What is the ratio of the time Xiaoming spends going to school to the time he spends coming back home? $\qquad$
【Analysis】Assuming the distance of a flat road $A B$ is $y$, the distance of an uphill road $B C$ is $2 y$, and the distance of a downhill road $C D$ is $y$, with the speeds on the flat, uphill, and downhill roads being $3 x, 2 x, 4 x$ respectively, then use the relationship between distance, speed, and time to find the ratio of the time taken to go to school and the time taken to return home.

【Solution】Solution: Time taken to go to school;
$$
\begin{array}{l}
\frac{y}{3 x}+\frac{2 y}{2 x}+\frac{y}{4 x} \\
=\frac{4 y+12 y+3 y}{12 x}, \\
=\frac{19 y}{12 x}
\end{array}
$$

Time taken to return home;
$$
\begin{array}{l}
\frac{y}{2 x}+\frac{y}{3 x}+\frac{2 y}{4 x}, \\
=\frac{6 y+4 y+6 y}{12 x}, \\
=\frac{16 y}{12 x},
\end{array}
$$

The ratio of the time taken to go to school to the time taken to return home is:
$$
\begin{array}{l}
\frac{19 y}{12 x}: \frac{16 y}{12 x}, \\
=\frac{19 y}{12 x} \times \frac{12 x}{16 y}, \\
=19: 16
\end{array}
$$

Answer: The ratio of the time taken to go to school to the time taken to return home is 19: 16.
Therefore, the answer is: 19: 16.