In martha's class 5/8 of the students walk to school and 1/8 of the students ride the bus. martha added the fractions and found the sum was 1/8 .which statement best describes the sum 1/8?

The answer would be C.  First, poor Martha added the fractions wrong.  The sum should be 6/8.  So her logic is the following:

1/8 + 5/8 = 1/8

This is not reasonable since 1) the sum is incorrect, and 2) according to the identity rule for addition, if you add 0 to a number, you get that number. (ie, A + 0 = A).  She ended up with the same number (1/8) after adding a number that is not 0 (5/8).