if your field is actually storing the characters 2-3, this will need to be a text field. If you need to sort your records using this field, that will be a problem. You may need to define a calculation field that returns number with something such as:
Getvalue ( Substitute ( "2-3" ; "-" ; ¶ ) ; 1 )
This gives you a field where, if you specify it in your sort order, sorts on the value to the left of the "-" character.
otherwise how could i store this information?
You could store it as two number fields, one for the minimum value and one for the maximum value. That gives you two number fields, but you can still display the data in your 2-5 format using merge fields or a calculation field that combines the values with the hyphen.