【Solution】Solution: A starts 20 minutes later, by which time B has already walked 10 minutes at a fast pace and 10 minutes at a slow pace (i.e., 15 minutes at a fast pace), and B starts 20 minutes earlier, which means B has already walked 20 minutes at a fast pace. Therefore, the midpoint should be at the $\frac{3}{4}$ point between 24 kilometers and 20 kilometers, i.e., 24 - (24-20) $\times \frac{3}{4}=21$ (kilometers) $21 \times 2=42$ (kilometers) Hence: The distance between A and B is 42 kilometers.
10. From 7:00 to 8:00 in the morning is the peak hour in a city, during which all vehicles travel at half their original speed. Every morning at 6:50, two people, A and B, start from points $A$ and $B$ respectively, heading towards each other, and meet at a point 24 kilometers from $A$. If A starts 20 minutes later, they meet exactly at the midpoint of $A B$; if B starts 20 minutes earlier, they meet at a point 20 kilometers from $A$. Therefore, the distance between $A$ and $B$ is $\qquad$ kilometers.