Question

Consider all numbers consisting of four different digits all between 1 and 9 . How many of these are odd

Answer 1

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