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

Explanation

To find the total number of 9-digit numbers which have all different digits, we can break down the problem into systematic steps.

### Step-by-Step Solution:

1. **Understanding the Digits**:
We have a total of 10 digits available: 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9. However, since we are forming a 9-digit number, we need to ensure that the first digit cannot be 0 (as it would not count as a 9-digit number).

2. **Choosing the First Digit**:
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