All of the answers must be able to be proven. The other scientists get together, see what the new guy did, and then they repeat what he did. If they come up with the same answer, everybody is happy. If the answer is different, someone did something wrong, and everyone starts all over again. There are no opinions which are considered scientific laws.
Quantitative statements are ones that can be proven through experiments.
Sherlock Holmes, that detective guy from the books, uses deductive reasoning to solve mysteries. If the premises are true, then the conclusion will also be true. You start by having a number of observations. It's in two parts. There is a problem to inductive reasoning, your conclusions have more information than the facts you use.