Assuming you are using combinations in the colloquial way (which is the mathematical "permutations" where order of selection does matter) to create a 3 digit number that does not start with 0, ie creating a number that is between 100 and 999 inclusive then:
If repeats are not allowed there are 3 × 3 × 2 = 18 possible numbers
If repeats are allowed, then there are 3 × 4 × 4 = 48 possible numbers.
If you are using combinations in the mathematical sense where order of selection does not matter and are creating groups of 3 digits, then:
If repeats are not allowed there are 4 possible groups
If repeats are allowed there are 20 possible groups.
There are twelve possible solutions using the rule you stated.
-8
1
10,000 combinations.
There are 15180 combinations.
You have 2 options for the first digit, 2 options for the second digit, etc. ... In total, that gives you 210 combinations.
Number of 7 digit combinations out of the 10 one-digit numbers = 120.
216
There are 840 4-digit combinations without repeating any digit in the combinations.
There are 5,040 combinations.
120 combinations using each digit once per combination. There are 625 combinations if you can repeat the digits.
There are 210 4 digit combinations and 5040 different 4 digit codes.
the answer is = first 2-digit number by using 48= 28,82 and in 3 digit is=282,228,822,822
Assuming no repeated digits, lowest first, 20; in any order 120; Allowing repeated digits: 216
There are twelve possible solutions using the rule you stated.
if its not alphanumeric, 999999 variations
-8