If the digits can be used more than once, then 900.
If not, then 648.
There are 60480 numbers.
5 x 10 x 5 = 250 different numbers, assuming there is no limit to each digits' use.
1 set
There are 5! = 120 such numbers.
There are 900 of them.
5040 different 4 digit numbers can be formed with the digits 123456789. This is assuming that no digits are repeated with each combination.
10,000
36
27 three digit numbers from the digits 3, 5, 7 including repetitions.
24
500
There are 60480 numbers.
840
There are 3024 of them.
180 of them.
There are 5*4*3 = 60 such numbers.
5 x 10 x 5 = 250 different numbers, assuming there is no limit to each digits' use.