A student evaluated - 4+x for x = - 9 1/2 and got an answer of 5 1/2. What might the student have done wrong?

When you add two negatives, there is no way you can get a positive answer.

What they did was change the - 9 1/2 to a positive when plugging it into the equation. That or the student believe that addition of negatives followed the same rules as multiplication/division.