how does 1-0.165 turn into 0.835?

     line up the decimal points and then subtract like normal.

             $$1.000\_

{0.165}$$

Because you are only taking a part of it away. Think of one as something as a whole. It can be a pie, person, whatever. If you take a slice of that pie, you will still have some left; it will just be a smaller amount. If you take a piece of one, it will  be a decimal.