Well if it was that easy, your world would look already different after reading the sentence before, right? But you are not some logical calculating system, where 1 + 1 = 2 always.

You are human. In your life, perception gives you situations, where one plus one equals zero....

Let's say that a company's stock trades for $100 and that the company has earnings per share (EPS) of $6.50 over the last 12 months. 

We can calculate a trailing ("last 12 months") P/E ratio for that stock by simply dividing the stock price ("P") by the EPS ("E"), so 100/6.50 equals about 1...