7 - 3 = 4, 8 - 5 = 3, 9 - 8 = 1

Conclusion: the difference of two positive numbers is always positive.

2 - 3 = -1

Oops.

If by difference, you mean the larger minus the smaller, the conclusion is true.

Technically, though, the difference is

   minuend
- subtrahend
-----------------
difference

So it matters which is which.

State a conclusion that seems reasonable.

You eat a new kind of fruit and suffer from hives for the first time in your life. A week later, you try the fruit and the hives recur. A month later, you have a similar experience.

Conclusion:

my first guess is you are allergic to that fruit.

Counterexample: Any difference between a smaller number and a larger one will produce a negative number. e.g. 3-7=-4

To understand why the difference of two positive numbers is always positive, let's take a closer look at the examples you provided:

1. 7 - 3 = 4: In this case, we start with a larger number (7) and subtract a smaller number (3). The result is a positive number (4).

2. 8 - 5 = 3: Similarly, we have a larger number (8) and subtract a smaller number (5). The result, again, is a positive number (3).

3. 9 - 8 = 1: Once more, we have a larger number (9) and subtract a smaller number (8). The result, as expected, is a positive number (1).

Based on these examples, we can conclude that when subtracting a smaller positive number from a larger positive number, the difference will always be a positive number. This is because subtracting a smaller number results in "taking away" less from the larger number, leaving more remaining. Therefore, the difference will always be positive.