103 = 1000 in all.
900 ,999 ,909
10 x 9 x 8 = 720 different "permutations"
If the first digit can be zero, there are 5,040. If the first digit can't be zero, there are only 4,536.
9
1000
There are 210 4 digit combinations and 5040 different 4 digit codes.
10,000
103 = 1000 in all.
900 ,999 ,909
10 x 9 x 8 = 720 different "permutations"
104 or 10000
If the first digit can be zero, there are 5,040. If the first digit can't be zero, there are only 4,536.
There are 10000 such codes. Each of the numbers 0-9 can be in the first position. With each such first digit, each of the numbers 0-9 can be in the second position. With each such pair of the first two digits, each of the numbers 0-9 can be in the third position. etc.
9
1,000 of them. The list of possibilities will look exactly like the counting numbers from 000 to 999 .
The possible 4 digit codes using the numbers 0-9 are every number between 0 and 9999. For numbers that have less than 4 digits, just precede the number with 0's. 10,000 possibilities