Kinds of Justification for Claims

How do we decide whether the following claims are true or not? What is the strongest kind of justification? What do we do when different kinds of justification come into conflict?

1. Elvis is alive.
2. 1 + 1 = 2
3. I (the person reading this sentence) exist.
4. God exists.
5. Water is composed of two atoms of hydrogen and one of oxygen.
6. It is wrong to murder babies for fun and profit.
7. It is snowing today.
8. The American economy will be stronger in 5 years than it is today.
9. Women are smarter than men.
10. John F. Kennedy was murdered in 1963 by Lee Harvey Oswald.