Question

Sally claims that it is easier to add two fractions if she
adds the numerators and then adds the denominators.
How can you help her?

Answer 1

I can't help Sally if she insists on making up her own rules.

Tell Sally she has to make sure there are common denominators first. Otherwise she will get the wrong answer.

Answer 2

Even then she's wrong:

3/2 + 5/2 = 8/2, not 8/4