1. When a car travels from point $A$ to point $B$, it spends $25 \%$ of the time on the uphill journey, $60 \%$ on the flat road, and the remaining time on the downhill journey. The time it takes to travel from $A$ to $B$ and back from $B$ to $A$ along the same road is the same, and its speeds uphill, downhill, and on the flat road are constant but different. How many times faster does the car travel downhill compared to uphill?
Answer: $5 / 3$.

Solution. If the speed of the car downhill is $x \neq 1$ times the speed uphill, then from the condition we have:

$$
\begin{aligned}
0.25+0.15= & 0.25 / x+0.15 x \quad \Rightarrow \quad 0.15 x^{2}-(0.25+0.15) x+0.25=0 \\
& \Rightarrow \quad(x-1)(x-5 / 3)=0 \quad \Rightarrow \quad x=5 / 3
\end{aligned}
$$

Answer to variant 2: $5 / 4$.

Answer to variant 3: 4/3.

Answer to variant 4: $7 / 4$.