Help needed.

I need your help!

My daughter had a math test yesterday. She came home today and made the following statements:

"I got a 97 on the Math test. The class average was 88."

It seems to me that an "an " is needed in front of 88. That is, The class average was an 88".

I tried to point out the inconsistency to her but she insisted that's how the teacher said it. 

What's your opinion?

Thanks a lot.