Well you have 10 possible numbers for the fist column(0-9) and 10 for the second, third, and fourth then you multiply those numbers. 10*10*10*10=10000 or 10^4=10,000. So there are 10,000 different combinations.
Digi.
The order of the digits in a combination does not matter. So 123 is the same as 132 or 312 etc. There are 10 combinations using just one of the digits (3 times). There are 90 combinations using 2 digits (1 once and 1 twice). There are 120 combinations using three different digit. 220 in all.
If the digits can repeat, then there are 256 possible combinations. If they can't repeat, then there are 24 possibilities.
9,000 - all the numbers between 1,000 and 9,999 inclusive. * * * * * NO. Those are PERMUTATIONS, not COMBINATIONS. Also, the question specified 4 digit combinations using 4 digits. The above answer uses 10 digits. If you start with 4 digits, you can make only 1 combination.
Using the word "combinations" in the English sense (as opposed to mathematical sense the expert has used) where it often used in the mathematical sense of the word "permutations": Assuming the hundreds digit must be at least 1 (eg 99 = 099 is not considered a three digit number), then: 9 x 10 x 10 = 900.
Number of 7 digit combinations out of the 10 one-digit numbers = 120.
1
The order of the digits in a combination does not matter. So 123 is the same as 132 or 312 etc. There are 10 combinations using just one of the digits (3 times). There are 90 combinations using 2 digits (1 once and 1 twice). There are 120 combinations using three different digit. 220 in all.
8877690
120 combinations using each digit once per combination. There are 625 combinations if you can repeat the digits.
Each digit can appear in each of the 4 positions. There are 9 digits, therefore there are 9⁴ = 6561 such combinations.
If the digits can repeat, then there are 256 possible combinations. If they can't repeat, then there are 24 possibilities.
Possible 5 digit combinations using 5 digits only 1 time is 5! or 5*4*3*2*1 or 120. Using 5 digits where numbers can be used 5 times is 55 or 3125.
9,999,876 is the greatest seven-digit number using four different digits.
9,000 - all the numbers between 1,000 and 9,999 inclusive. * * * * * NO. Those are PERMUTATIONS, not COMBINATIONS. Also, the question specified 4 digit combinations using 4 digits. The above answer uses 10 digits. If you start with 4 digits, you can make only 1 combination.
If you use them only once each, you can make 15 combinations. 1 with all four digits, 4 with 3 digits, 6 with 2 digits, and 4 with 1 digit. There is also a combination containing no digits making 16 = 24 combinations from 4 elements.
Using the word "combinations" in the English sense (as opposed to mathematical sense the expert has used) where it often used in the mathematical sense of the word "permutations": Assuming the hundreds digit must be at least 1 (eg 99 = 099 is not considered a three digit number), then: 9 x 10 x 10 = 900.
Number of 7 digit combinations out of the 10 one-digit numbers = 120.