6!
5040 different 4 digit numbers can be formed with the digits 123456789. This is assuming that no digits are repeated with each combination.
There are 3024 of them.
180 of them.
There are 60480 numbers.
840
24
500
27 three digit numbers from the digits 3, 5, 7 including repetitions.
There are 5*4*3 = 60 such numbers.
1 set
There are 5! = 120 such numbers.
The number 1234567890 can create about 39 of 40 4 digit numbers.