9. Two people, A and B, agree to meet at a certain place within 10 days. They agree that the one who arrives first will wait for the other, but can leave after waiting for 3 days. If they are equally likely to arrive at the destination within the limit, then the probability that these two people will meet is $\qquad$ .
9. $\frac{51}{100}$

Let A and B arrive at a certain place on the $x$-th and $y$-th day respectively, where 0 $\leqslant x \leqslant 10,0 \leqslant y \leqslant 10$. The necessary and sufficient condition for them to meet is $|x-y| \leqslant 3$. The point $(x, y)$ is distributed within the square $O A B C$, and the basic event $S_{1}$ is within the shaded area between the two lines $x$ $y= \pm 3$. 
Therefore, the required probability is $P=\frac{100-(10-3)^{2}}{100}=\frac{51}{100}$.