Well, honey, if you want to know the number of 4-digit combinations with no repeated numbers, it's pretty simple. You start with 9 choices for the first digit (can't be 0), then 9 choices for the second digit (can't repeat the first), 8 choices for the third digit, and finally 7 choices for the fourth digit. Multiply those together and you get 4536 possible combinations. Easy peasy lemon squeezy!
27 three digit numbers from the digits 3, 5, 7 including repetitions.
24
A lot. And there is akways the code. 1234
Five numbers (5, 6, 7, 8, 9) can be selected for each of the 5 digits. So, there are 5*5*5*5*5 or 55 or 3125 five digit numbers.
There are 9 1-digit numbers and 16-2 digit numbers. So a 5 digit combination is obtained as:Five 1-digit numbers and no 2-digit numbers: 126 combinationsThree 1-digit numbers and one 2-digit number: 1344 combinationsOne 1-digit numbers and two 2-digit numbers: 1080 combinationsThat makes a total of 2550 combinations. This scheme does not differentiate between {13, 24, 5} and {1, 2, 3, 4, 5}. Adjusting for that would complicate the calculation considerably and reduce the number of combinations.
757
823543
720 (10*9*8)
625 if numbers can have leading 0s, 500 otherwise.
9x9x8x7x6x5x4x3 =1632960
There are 5! = 120 such numbers.
81
9x9x8x7x6x5 = 81x56x30 = 136080
5040 different 4 digit numbers can be formed with the digits 123456789. This is assuming that no digits are repeated with each combination.
162
There are 4 possible numbers if the digits are not repeated; 18 if they are. Those are 3-digit numbers, assuming that zero would not be a leading digit. If zero is allowed for a leading digit, then you can have 6 for the non repeated, and 27 if repetition.
27 three digit numbers from the digits 3, 5, 7 including repetitions.