can't use forward slash in numbers

I am having a very strange problem in Numbers, after updating my system to El Capitan yesterday. I am trying to do a simple division in numbers but every time I type the forward slash to divide, it puts in a plus sign, so I can't get it to work at all. I've tried it in Excel and it works fine. I have tried using both the forward slash under the question mark, and the one on the numbers keypad. When I copy the formula into numbers from word, in changes the slash to a plus sign again.

What do I do now?

Thanks for any help.