How many different numbers of six digits each can be formed from the digits 4, 5, 6, 7, 8, 9 when repetition of digits is not allowed?

Explanation

To determine how many different six-digit numbers can be formed from the digits 4, 5, 6, 7, 8, and 9 without allowing repetition of digits, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Digits Available**:
We have the digits 4, 5, 6, 7, 8, and 9. This gives us a total of 6 unique digits.

2. **Determine the Number of Digits to be Used**:
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