how many whole numbers less than 100 does the digit 9 appear at least once??

Answer 1

9, one of these
19 , 29 ..... 89 eight of these
90 ..... 99 ten of these

Now wait a minute, you could do this problem better than I can with old fossilized brain.

Answer 2

looked at another way:

How many numbers can be formed with no 9

single digit: 8
2 digits: 8*9 = 72
total with no 9's = 80

so the numbers that do have a 9 is 99-80 = 19, like Damon had above.

Answer 3

20