Both fractions in the expression 1/3 + 1/3 are examples of

For this case we have the following expression:
 
 We observe that the numerator in both fractions is smaller than the denominator.
 Therefore, we are in the presence of two proper fractions.
 Since the denominator of both fractions is equal, then the result is given by:
 
 The numerators are added and the denominator is the same.
 The result is also a proper fraction because the numerator is smaller than the denominator.