Write an expression for the product of a two-digit number, between 10 and 99, and a three-digit number, between 100 and 999, where the result is greater than 4000 but less than 6000.

An expression that would meet the criteria provided can be written with variables to represent the two-digit and three-digit numbers. Let's use `x` to represent the two-digit number and `y` to represent the three-digit number.

Given that `x` is a two-digit number, it can range from 10 to 99, and `y`, as a three-digit number, ranges from 100 to 999. We want their product to be greater than 4000 but less than 6000.

The expression for their product would be `x * y`, and the constraints can be expressed as inequalities:

4000 < x * y < 6000

Now, let's find a possible pair of numbers `x` and `y` that would satisfy this inequality. It's a bit tricky to find specific numbers without trial and error, but we know that the lower bound of `x` (10) and the lower bound of `y` (100) give a product of 1000, which is too low. Similarly, the upper bounds of `x` (99) and `y` (999) give a product that is too high.

However, a reasonable guess might be to try a two-digit number closer to the middle of its range (around 50) and a three-digit number at the lower end of its range (just above 100).

For example, if we select `x = 50` and `y = 80`, the product is 4000, which is our lower limit. Since we want the product to be just above 4000, we need to increase one of the numbers slightly.

If we pick `x = 55` and `y = 80`, the product is 4400, which is in our desired range. Thus, we have a pair of numbers that satisfies the given criterion:

x = 55 y = 80

The expression for their product is x * y = 55 * 80 = 4400.