Everybody at a company is assigned a unique 9 digit ID. How many unique IDs exist?

3,265,920 unique ID exist.

Explanation:

The nine digits are from 0 to 9, there are ten bits from 0 - 9,

0, 1, 2, 3, 4, 5, 6, 7, 8, 9

The first is select from the highest bit (9), and the second is selected at random from 0 - 9, the third bit to the last must be unique and different from each other;

number of unique IDs = 9 * 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2

Multiplying the nine bits of unique IDs = 3,265,920.