20. (5 points) Cars A and B start from locations $A$ and $B$ respectively, heading towards each other. At the start, the speed ratio of A to B is 5:4. After they meet, A's speed decreases by $20\%$, and B's speed increases by $20\%$. As a result, when A reaches location B, B is still 10 kilometers away from location A. Therefore, the distance between $A$ and $B$ is $\qquad$ kilometers.
【Solution】Solution: After meeting, the speed ratio of A and B is: $[5 \times(1-20 \%)]:[4 \times(1+20 \%)]=5$ :
$$
\begin{array}{l}
10 \div\left(1-\frac{4}{4+5}-\frac{4}{9} \times \frac{6}{5}\right), \\
=10 \div \frac{1}{45}, \\
=450 \text { (km); }
\end{array}
$$

Answer: The distance between A and B is 450 km.
Therefore, the answer is: 450 .