Total number of natural numbers less than 4000 formed with digits 0,1,...
Total number of natural numbers less than 4000 formed with digits 0, 1, 2, 3, 4, 5, and 8 can be found by considering the following cases:
1. Numbers with 1 digit:
- We can choose any digit from 0, 1, 2, 3, 4, 5, and 8, so there are 7 choices.
- Therefore, there are 7 numbers with 1 digit.
2. Numbers with 2 digits:
- The first digit can be any digit from 1, 2, 3, 4, 5, and 8, so there are 6 choices.
- The second digit can be any digit from 0, 1, 2, 3, 4, 5, and 8, so there are 7 choices.
- Therefore, there are 6 * 7 = 42 numbers with 2 digits.
3. Numbers with 3 digits:
- The first digit can be any digit from 1, 2, 3, 4, 5, and 8, so there are 6 choices.
- The second digit can be any digit from 0, 1, 2, 3, 4, 5, and 8, so there are 7 choices.
- The third digit can be any digit from 0, 1, 2, 3, 4, 5, and 8, so there are 7 choices.
- Therefore, there are 6 * 7 * 7 = 294 numbers with 3 digits.
4. Numbers with 4 digits:
- The first digit can be any digit from 1, 2, 3, 4, 5, and 8, so there are 6 choices.
- The second digit can be any digit from 0, 1, 2, 3, 4, 5, and 8, so there are 7 choices.
- The third digit can be any digit from 0, 1, 2, 3, 4, 5, and 8, so there are 7 choices.
- The fourth digit can be any digit from 0, 1, 2, 3, 4, 5, and 8, so there are 7 choices.
- Therefore, there are 6 * 7 * 7 * 7 = 2058 numbers with 4 digits.
Adding up the numbers from each case:
7 + 42 + 294 + 2058 = 2401
Therefore, the total number of natural numbers less than 4000 formed with digits 0, 1, 2, 3, 4, 5, and 8 is 2401.
Hence, the correct answer is option D) none.