about 12
10,000 combinations.
There are 5,461,512 such combinations.
The answer will depend on how many digits there are in each of the 30 numbers. If the 30 numbers are all 6-digit numbers then the answer is NONE! If the 30 numbers are the first 30 counting numbers then there are 126 combinations of five 1-digit numbers, 1764 combinations of three 1-digit numbers and one 2-digit number, and 1710 combinations of one 1-digit number and two 2-digit numbers. That makes a total of 3600 5-digit combinations.
64
Number of 7 digit combinations out of the 10 one-digit numbers = 120.
If every number can be used as many times as you like, there are 104 = 10000 different combinations. If each number can only be used once, there are 9!/(9 - 4)! = 5040 combinations.
factorial six tat is 6*5*4*3*2*1=720 combinations
I am assuming you mean 3-number combinations rather than 3 digit combinations. Otherwise you have to treat 21 as a 2-digit number and equate it to 1-and-2. There are 21C3 combinations = 21*20*19/(3*2*1) = 7980 combinations.
It depends on how many digit you are choosing from.
6 of them.
starting at 1111 and going to 9999, there are 9*9*9*9 combinations (1...9 for each digit) = 6561
99. Each of the numbers in the list can only be used by itself otherwise you would get a 4-digit (or longer) number.