How many five digit telephone numbers can be constructed using the digits 0 to 9. If each numbers starts with 67 and no digit a appears more than once?

Explanation

To solve the problem of how many five-digit telephone numbers can be constructed using the digits 0 to 9, starting with 67 and ensuring that no digit appears more than once, we can follow these steps:

### Step-by-Step Solution:

1. **Identify Fixed Digits**: The first two digits of the telephone number are fixed as "67". Therefore, we only need to determine the last three digits of the five-digit number.

2. **Available Digits**: The digits available for selection are from 0 to 9, which gives us a total of 10 digits. However, since the first two digits are "6" and "7", we cannot use these digits again. This leaves us with the following available digits: 0, 1, 2, 3, 4, 5, 8, 9. Thus, we have 8 digits remaining.

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