24
There are 5*4*3 = 60 such numbers.
It is possible to create a 3-digit number, without repeated digits so the probability is 1.
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.
The largest 10-digit number with no digit repeated is 9876543210 !
24
500
There are 7,290 different 4-digit numbers that can be formed from the digits 1-9 without repetition.
There are 5*4*3 = 60 such numbers.
1 set
It is 120 if the digits cannot be repeated.
There are 5! = 120 such numbers.
3x3x3=27
4*3*2*1 = 24
48 of them if digits may not be repeated. 100 if they can.
36
6*6*3 = 108 numbers.