It is: 9C7 = 36
66
In other words, how many 4 digit combination locks are there using the digits 0-9 on each wheel. There are 10×10×10×10 = 10⁴ = 10,000 such combinations.
There are 9C3 = 84 combinations.
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.
There are 9999 possible combinations starting from 0000 to 9999
It is: 9C7 = 36
66
10,000
15
There are 59049 combinations, all the way from 11111, 11112 through 99998, 99999. There are too many to list here.
Through the magic of perms and coms the answer is 729
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.
In other words, how many 4 digit combination locks are there using the digits 0-9 on each wheel. There are 10×10×10×10 = 10⁴ = 10,000 such combinations.
If there are no restrictions on duplicated numbers or other patterns of numbers then there are 10 ways of selecting the first digit and also 10 ways of selecting the second digit. The number of combinations is therefore 10 x 10 = 100.
There are 1,120,529,256 combinations.