2. (1993 National High School Competition Question) There are 900 three-digit numbers, $100, 101, \cdots, 999$. When printing these three-digit numbers on cards, for example, 198 looks like 861 when flipped, while some cards do not, such as 531 which looks like IE9 when flipped. Therefore, some cards can be used for two numbers, thus the maximum number of cards that can be saved is $\qquad$.
2. 34. The digits that remain natural numbers when inverted are only $0,1,6,8,9$, and the hundreds and units digits cannot be 0. Therefore, such three-digit numbers have $C_{4}^{1} \times C \times C_{1}^{1}=80$ in total, but among them, some three-digit numbers remain the same when inverted (such as 619). The tens digit of such numbers can only be 0, 1, 8, and the hundreds and units digits can only be $1,6,8,9$, and once the units digit is determined, the hundreds digit is also determined. There are $C_{3} C_{1}^{1}=12$ such numbers. Therefore, the maximum number of cards that can be saved is $\frac{1}{2}(80-12)=34$.