What is the correct to write and/or? I have seen it written "and or" as two separate words and I think it looks odd.
You'd be hard pressed to find a style guide that doesn't admonish you to drop “and/or” and choose either “and” or “or.”
In writing either and or or is usually adequate.
If a greater distinction is needed, another phrasing is available : X or Y, or both.
It is more common in technical,business,and legal writing.
There is no correct way; it depends on what style guide you are using.
However, at least in AmE, and/or is the vastly more common construction. If in doubt, I would choose and/or.
For more information, I'll point you to Wikipedia: http://en.wikipedia.org/wiki/And/or
"and/or" has the same logical value as "or", I always use "or" which is simpler and better looking. In fact, the slash sign "/" is not even part of the standard punctuation and looks terrible when replacing the comma in normal text. Another reason for discouraging "/" is its ambiguous interpretation: "A/B" could mean "A or B", but also "either A or B" (what logicians call an "exclusive or", sometimes encoded as "xor" as in the Latin "aut" as opposed to "vel", which is the usual inclusive "or").
In writing the phrase and/or, for example in a sentence as: I need to purchase a new item and/or return this one. the sentence would literally translate to: I need to purchase a new item and and or or return this one.
To properly designate the intention of "and/or" it would be written: I need to purchase a new item/return this one.
Nonetheless, the usage of the phrase is highly regarded as inappropriate/poor writing.