Are "w/o", "w/", "b/c" common abbreviations in the US?

I remember when staying a few months in the US years ago that I saw some people using the abbreviations below. However, I can't exactly remember in which contexts I encountered them, (whether I saw my teachers using them when writing something on the board, in papers or in personal notes etc.)

So my question is: Are those abbreviations below commonly used and in which contexts is it okay to use them (e.g. formal texts, personal notes,... or better only used in personal note taking?)

• w/o without
• w/ with
• b/c because

PS: Are there similar abbreviations that are commonly used?

Both "w/" and "w/o" were common, very informal, U.S. abbreviations in correspondence, and in tight spots on data tables, until recently. "C/o" has always been used in addressing letters to third parties: "John Jones, c/o Smith family..."

The other "slash/shilling mark" abbreviations were so uncommon that they usually were not used because of lack of clarity.

I personally use only "c/o", "w/" and "w/o" of all the abbreviations shown on this page. (Except for very limited use of the technical jargon abbreviations: I/O, A/C.)

English writing often uses slashes to form two-letter abbreviations, plus the one-letter w/ – some examples, roughly in order of frequency:

• I/O – “input/output”
• w/ – “with”
• c/o – “care of”
• A/C – “air conditioning”
• w/o – “without”
• R/C – “remote control”
• b/c – “because”

Like most abbreviations, these are less common in formal writing, although some of them (like I/O) appear often in technical writing. Some are uncommon even in informal writing; I've only seen b/c in things like text messages and tweets, for example, and those usually leave out the slash.

I would say all three are fairly common, though not necessarily "correct".

I think almost everyone will understand all of them, but I would avoid them, particularly in formal contexts. Of course in personal note-taking you can use whatever shorthands you like. 

Along with TrevorD, I'm in the UK.

I've seen w/o for without and w/ for with, but not b/c.

They are not suitable for formal use.

It's potentially of interest that the Pitman shorthand symbol for w resembles w/ and is often used on its own to mean with.

I can't answer for what is common usage in the US, but in the UK:

• I've seen w/o for without
• I don't recall ever seeing w/ or b/c

I certainly wouldn't say that they are in common 'public' usage, and would suggest they are best reserved for private usage, note-taking, etc.