According to your comment the regex you are looking for is this:
http://www.regexper.com/#%5E(%5B1-9%5D%5B0-9%5D*)((%5Cs((%5B1-9%5D%5B0-9%5D*)%5C%2F(%5B1-9%5D%5B0-9%5D*)))*%7C(%5C%2F(%5B1-9%5D%5B0-9%5D*))*)%24[
^]
^([1-9][0-9]*)((\s(([1-9][0-9]*)\/([1-9][0-9]*)))*|(\/([1-9][0-9]*))*)$
Now let break it apart...
^([1-9][0-9]*)$
This declare a group of numbers where the first digit must be between 1 and 9 and the second can be from 0 to 9 - optionally...
^(\s(([1-9][0-9]*)\/([1-9][0-9]*)))*
This part allows (means this is optional) a single whitespace (\s) and two numbers (like the first one) separated by /...
^(\/([1-9][0-9]*))*$
The last part allows (again it is optional) a / and a number, same like at the beginning...
This will allow 2 and 2/3 and 2 2/3 also