Thanks! Actually, we did a similar thing as you suggested.

My daughter did not care - basically she did not care about her grade. We told her we did not agree with her teacher's answers and asked her what she thought. She thought 9 was the correct answer, but she choose to let it go.

But I, as the parent, am concerned.I truly believe the teacher does not understand the concept.It may sounds shocking, but I believe it that.The least I can do is to find her another teacher.