5
45.
There are 5*4*3*2 = 120 such numbers.
Just one. In a combination, the order of the digits does not matter.
106 or a million.
Number of 7 digit combinations out of the 10 one-digit numbers = 120.
90
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.
There are 1140 five digit combinations between numbers 1 and 20.
You would get 4!/2! = 12 combinations.
There are 840 4-digit combinations without repeating any digit in the combinations.
7
56 combinations. :)
Any 6 from 51 = 18,009,460 combinations
5
45.
There are 5*4*3*2 = 120 such numbers.