How many numbers are there between 100 and 1000 such that every digit is either 7 or 9 ?

Explanation

To solve the problem of how many numbers between 100 and 1000 have every digit as either 7 or 9, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Range**:
We need to find three-digit numbers between 100 and 1000. This means we are only considering numbers that have three digits.

2. **Determine the Digits**:
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