How many numbers are there between 100 and 1000 which have exactly one of their digits as 7?

Explanation

To find how many numbers between 100 and 1000 have exactly one digit as 7, we can break the problem down into three cases based on the position of the digit 7 in the three-digit number.

### Step-by-Step Solution:

**Step 1: Understand the range of numbers**
- The numbers we are considering are between 100 and 1000, which means we are dealing with three-digit numbers.

**Step 2: Case 1 - 7 in the first position**
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