3 个数的和是 555。第 1 个数是一位数，第 2 个数是两位数，第 3 个数是三位数。 第 2 个数和第 3 个数之间最小可能的差是多少？ 答案：___

1. Express the difference in terms of the numbers and identify the condition for the minimum difference.

Let the 1-digit number be $a$, the 2-digit number be $b$, and the 3-digit number be $c$.
We are given $a + b + c = 555$.
We want to find the smallest possible difference between $c$ and $b$, which is $c - b$.
From the sum, $c = 555 - a - b$.
Substitute this into the difference: $c - b = (555 - a - b) - b = 555 - a - 2b$.
To make $555 - a - 2b$ as small as possible, we must make $a$ and $b$ as large as possible.

2. Determine the maximum possible values for the 1-digit and 2-digit numbers.

The maximum value for a 1-digit number is $a = 9$.
The maximum value for a 2-digit number is $b = 99$.

3. Calculate the 3-digit number and the minimum difference.

Using the maximum values, $c = 555 - 9 - 99 = 447$.
The difference is $c - b = 447 - 99 = 348$.
Alternatively, using the expression: $555 - 9 - 2(99) = 555 - 9 - 198 = 348$.