The difference between two whole numbers is 45. One of them is a 2-digit number and the other is a 3-digit number. What is the smallest possible sum of the two numbers? Ans: ___

1. Set up the relationship between the two numbers

Let the 2-digit number be $x$ and the 3-digit number be $y$.
Since $y$ has 3 digits and $x$ has 2 digits, $y > x$.
The difference is $45$, so $y - x = 45$, which means $y = x + 45$.

2. Find the smallest possible values for the numbers

To find the smallest possible sum $x + y$, we must make $x$ and $y$ as small as possible.
The smallest possible 3-digit number is $100$.
If $y = 100$, then $x = 100 - 45 = 55$.
$55$ is a valid 2-digit number.

3. Calculate the smallest possible sum

Smallest sum = $55 + 100 = 155$.