how many whole numbers less than 100 does the digit 9 appear at least once??
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.
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.
20
To find out how many whole numbers less than 100 contain the digit 9 at least once, we can use a simple approach:
1. Start by listing all the numbers from 1 to 99.
2. Go through each of these numbers and check if the digit 9 appears in them.
3. Count the numbers that contain the digit 9 at least once.
Let's follow these steps:
1. List the numbers from 1 to 99:
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, ...
2. Check if the digit 9 appears in each number:
- The number 9 contains the digit 9.
- The numbers 19, 29, 39, 49, 59, 69, 79, 89, and 90 contain the digit 9 in the tens place.
- The numbers 91, 92, 93, 94, 95, 96, 97, 98, and 99 contain the digit 9 in the ones place.
3. Count the numbers that contain the digit 9 at least once:
We have a total of 9 numbers (9, 19, 29, 39, 49, 59, 69, 79, 89) where the digit 9 appears in the tens place and 9 numbers (9, 19, 29, 39, 49, 59, 69, 79, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99) where the digit 9 appears in the ones place. However, the number 9 appears in both categories, so we should count it only once.
Therefore, the total count of whole numbers less than 100 containing the digit 9 at least once is 18.