6. "Ascending numbers" are natural numbers where each digit is greater than the one to its left (such as 2578). The probability of randomly selecting a two-digit "ascending number" greater than 37 is $\qquad$
6. $\frac{17}{36}$ There are $C_{9}^{2}$ two-digit ascending numbers in total, those greater than 37 can be divided into two categories, one is $\overline{3 b}$, with a total of 2. The other category is $\overline{a b}, 4 \leqslant a<b \leqslant 9$, with a total of $C_{6}^{2}$. Therefore, the required probability is $\frac{2+C_{6}^{2}}{C_{9}^{2}}=\frac{17}{36}$.