Thank you Zen!!! Believe it or not, this answer was going to keep my DS out of the differentiation math group they are starting. She called me to tell me that she's going to let him anyway because she does think he needs it even though he really shouldn't be in the group b/c he answered this question on the pre-test wrongly. She was making it sound like he really shouldn't be in the group b/c he did not under stand the "deeper" concepts that this problem is designed to highlight. (I just vomited a little in mouth I think). So that pdf will come in very handy!