1
There are 6804 such numbers.
The answer will depend on how many digits you have at your disposal. Working with the 10 digits, and barring leading zeros, there are 8,877,690 numbers.
To find the total number of seven-digit numbers that contain the number seven at least once, we can use the principle of complementary counting. There are a total of 9,999,999 seven-digit numbers in total. To find the number of seven-digit numbers that do not contain the number seven, we can count the number of choices for each digit (excluding seven), which is 9 choices for each digit. Therefore, there are 9^7 seven-digit numbers that do not contain the number seven. Subtracting this from the total number of seven-digit numbers gives us the number of seven-digit numbers that contain the number seven at least once.
27: 077,177,277,377,477,577,677,877,977,717,727,737,747,757,767,777,787,797
17
16000
There are 9000 4-digit numbers. 8*9*9*9 = 5832 of them do not contain a 5 The remaining 3168 contain a 5.
1
-2
In base ten, there are 9000 four digit number, the numbers are from 1000 to 9999. If you allow leading zeros, then there are 10000 numbers. [0000 - 9999]
three zeros
-5
It would help to know which digit. 0 appears in 9 numbers and each of the others in 18 numbers.
None. The only way for it to be possible would be 3 zeros which is not considered a 3 digit numbers.
A Thousand digit number will have 999 zeros
4 All of them are significant. Only zeros are potentially insignificant. And that's only when your numbers either start with zeros like 0.001 (1 significant digit 1) or end with zeros 13.0000 (2 significant digit, 13). Any zeros between non-zero numbers are significant.