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?