Without using the Character Map program or the Insert Symbol command in Word is to use the "insert unicode character" command, which is done by typing the unicode code then immediately hitting ALT+X (no space, nothing after the code).
The one third symbol is unicode character 2153, so if you type 2153 immediately followed by ALT+X you'll get a on third (in Arial, but not all fonts have that symbol).
The two-thirds symbol is 2154.
Here are the available fraction symbols and their unicode code:
fraction numerator one 215F (which gives you one with the slash as one character, after which you can then type in what you want as a denominator)
~ William James