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?

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.

Even then she's wrong:

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

To help Sally understand if her claim is correct, we can break down the process of adding fractions step-by-step:

1. First, explain to Sally that when adding fractions, the denominators must be the same. If they are not the same, we need to find a common denominator before adding.

2. Once the denominators are the same, you can help Sally by explaining that adding the numerators is correct when the fractions have the same denominator.

3. To demonstrate this, use an example where the denominators are already the same. For instance, let's say Sally wants to add 1/4 and 3/4. In this case, both fractions already have the same denominator, so she can simply add the numerators: 1 + 3 = 4. The result is 4/4, which simplifies to 1.

4. Next, you should introduce an example where the fractions have different denominators. For example, Sally wants to add 2/3 and 1/6. In this case, you can point out that the denominators are different, so they need to be made the same. To do this, help her find the least common multiple (LCM) of 3 and 6, which is 6.

5. Once both fractions have the same denominator, explain to Sally that she can add the numerators and keep the denominator unchanged. So, in this example, the sum would be 2 + 1 = 3. The result is 3/6, which can be simplified to 1/2.

By explaining and illustrating these steps, you can help Sally understand that adding the numerators and denominators separately is correct only when the fractions have the same denominator.