If the digits may be repeated, and if the number may begin with a zero, then it's just all of
the counting numbers up to 999,999,999.
If it can't begin with a zero, then you have to throw away the first 99,999,999 and there can
only be 900,000,000.
If you allow the number 000000000, then there are 109 or a billion numbers.
It is possible to create a 3-digit number, without repeated digits so the probability is 1.
0000-9999 (10x10x10x10 or 104) = 10,000 possible combinations allowing for repeated digits. If you are not able to repeat digits then it's 10 x 9 x 8 x 7 or 5,040 possible combinations without repeated digits.
There are 5*4*3 = 60 such numbers.
24
27 three digit numbers from the digits 3, 5, 7 including repetitions.
9x8x7x6x5x4x3x2x1 or 9! which equals 362880 possible combinations if no digits are repeated
It is possible to create a 3-digit number, without repeated digits so the probability is 1.
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.
6*5*4*3*2*1=720 possible numbers
Infinite. If numbers can be repeated, the list could go on nonstop.
98,764
0000-9999 (10x10x10x10 or 104) = 10,000 possible combinations allowing for repeated digits. If you are not able to repeat digits then it's 10 x 9 x 8 x 7 or 5,040 possible combinations without repeated digits.
763920
There are 5*4*3 = 60 such numbers.
757
With repeated digits, 43 = 64 Without repeated digits, 4*3*2 = 24
24