Question

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

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

Answer 1

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.

Answer 2

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:

Answer 3

my first guess is you are allergic to that fruit.

Answer 4

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