Answer:
1680
Step-by-step explanation:
Considering repeatition is not allowed.
We can use permutation to reach to the required answer.
Consider four digits to be placed in four boxes. Now for the number to be odd, unit digit must be odd. Therefore, unit digit can only be filled by 1, 3, 5,7, or 9. That is 5 ways. Now, other three boxes can be filled with 8, 7 and 6 ways respectively.
Therefore, Total numbers = 5×8×7×6 = 1680
