CounterExamples and Inductive Reasoning and Conjectures?

Make a Conjecture for Each Scenario. Show your Work
- the sum of the first 100 positive even numbers,
- the sum of an even and odd number.
- the product of two odd numbers.

FInd One CounterExample to show that the conjecture is false.
-the difference of two integers is less than either integer.

Please and Can you Explain Each One and why it is that. And Can you show me How to set it up so it will be Easier in the Future.