Find the total number of 9-digit numbers which have all different digits.

Explanation

To find the total number of 9-digit numbers that have all different digits, we can follow these steps:

### Step 1: Understand the constraints
A 9-digit number cannot start with the digit '0'. Therefore, the first digit must be one of the digits from 1 to 9. This gives us 9 options for the first digit.

**Hint:** Remember that the first digit of a number cannot be zero.

### Step 2: Choose the first digit
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