meta keywords not in body of page

How literally does Google interpret this?

[directrix]

I've heard that Google frowns upon and can penalize pages that have meta keywords which do not appear in the body of the page. I can understand their reasoning, but I wonder how literally they interpret this.

For example, assume I run a mathematically oriented site. On the home page I plan to specify the meta keywords shown below. The word "maths" will not actually appear in the page text at all, but I include it in the keywords as it's closely related to the theme of the page and the site. In view of this:

1) Is Google likely to penalise the page or site?
2) Will Google view so many "math-stemmed" words as spammy? Or will it see them all as different words?
3) Does Google place any weight on the meta keywords, anyway?
4) For all of the above, what about other search engines, such as Yahoo or msn?

<meta name="Keywords" content="mathematical puzzles,mathematics,math,maths,algebra,..." />