Answer:
3,024
Step-by-step explanation:
There are digits 1, 2, 3, 4, 5, 6, 7, 8, and 9 (9 digits in total).
The first digit of 4-digit number can be selected in 9 different ways (any of given digits can be chosen), then 8 digits remain.
The second digit can be selected in 8 different ways, then 7 digits remain.
The third digit can be selected in 7 different ways, then 6 digits remain.
The fourth digit can be selected in 6 different ways.
In total, there are
[tex]9\cdot 8\cdot 7\cdot 6=3,024[/tex]
different ways.
