How many 3 digit numbers can be made by using one digit?

There are 10 possible digits (0 through 9). However, for a 3-digit number, the first digit cannot be 0, so it must be one of the digits from 1 to 9. Therefore, there are 9 valid choices for the first digit. If using only one digit to form the entire number, the only valid 3-digit numbers would be 111, 222, ..., 999, resulting in a total of 9 three-digit numbers.