I know they both roughly mean "example", but which one should I use, and when?
E.g. is short for exempli gratia and stands for "for example". Ex., if used to mean the same, is incorrect. Mostly ex. is used as short for exercise and not "for example".
"Ex." is not very common, but it may be used to refer to a cited example, eg "See ex. 3".
"E.g." is much more common, and is used to introduce an example, or series of examples. In speech, it is usually replaced by "for example".
protected by tchrist Dec 2 '14 at 3:20
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