良好网格

注意$a <= 0$，为$\min(0,b) <= 0$。此外，我们还看到$b >= 0$，如$\max(0, a) >= 0$。因此，问题的解就是$a <= 0$和$b >= 0$的概率。 $a$和$b$共有$21^2 = 441$可供选择的方式。其中，$a$ 和 $b$ 各有 11 个选择，即 $a <= 0$ 和 $b >= 0$，因此我们有 $\frac{11^2}{21^2} = \frac{121}{441}$ 的概率。

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Original Explanation

Note that $a <= 0$, as $\min(0,b) <= 0$. Furthermore, we also see that $b >= 0$, as $\max(0, a) >= 0$. Therefore, the solution to the problem is the probability that $a <= 0$ and $b >= 0$. There are $21^2 = 441$ total ways in which $a$ and $b$ can be selected. Of those, we have 11 choices for each $a$ and $b$, as $a <= 0$ and $b >= 0$, leaving us with a probability of $\frac{11^2}{21^2} = \frac{121}{441}$.