EDIT: Your Mongoose Paver uses 700C tires, a.k.a. 622mm, and sometimes known as a 28" tire when the 28 is followed with a fractional size.

You can't answer any of those questions due to their extreme generality. First read the Sheldon Brown page linked above (or if you want the utterly, most comprehensive chart of virtually every wheel size to exist, http://www.bikecult.com/works/wheelsizes.html), then read the markings on your tires and rims.

Once you're clear as to what you have, re-phrase your question so that there is no doubt as to what you wish to do to X size tire on Y size rim. As it is now, your three tire sizes can be interpreted as follows:

There are multiple sizes - diameter wise - that are known as 28". Most commonly termed 28" tire is the 28x1-1/2, a.k.a. 700B. 635mm in diameter, designed for English roadsters. It is unlikely that you have this rim or tire. The second tire to be commonly badged - today - is the 700C tire, as DieselDan indicates. 700C is also known as 622mm, or 28x(a certain fractional size).

Generally, 27" as known today is always considered 630mm in diameter regardless of the tire - the other two existing variants are unusual enough to be ignored in this case.

The "700" term can be applied to the virtually extinct 700A and 700D sizes, or the more common 700B (known better as a 28x1-1/2/635mm tire used on English roadsters), or the presently popular 700C size, which is technically 622mm.

P.S.: There is no such thing as a 28x1.75. Either a 26x1.75 or a 28x(fractional size).

-Kurt