It's better to skip a question entirely than to get it wrong (in most cases).
I think for the mathematics section, it's different, but it should be clearly delineated to you before the test. You get credit for what you attempted. All it is is a basic, general test. If you can take a test in any subject, you'll do fine. It doesn't count against you or anything, so you should just do your best and see how good that is.