9. The teacher needs to make 100 number cards from 1 to 100. When printing, the printer malfunctioned and printed the digit "1" as "7". So, $\qquad$ number cards were printed incorrectly.
【Answer】 19
【Analysis】We classify such numbers into three categories according to their digits. The first category is single-digit numbers, which only include 1; two-digit numbers can be further divided into two types, one being 11, 12, 13...19, totaling 9 numbers, and the other being 21, 31, ... , 91, totaling 8 numbers; the third category is three-digit numbers, which only include 100, so in total, there are $1+9+8+1=19$ cards that will be marked incorrectly.