A unit of 1 is singluar. Anything else is plural.
1 apple. 2 apples. 0 apples.
10 degrees. -30 degrees. 1 degree.
At least that's how I've always said it.
No. Vulgar fractions have their own rules; they aren't used like ordinary numbers. However, zero point five apples are not enough for the salad (not, of course, that anyone would say this).Wait, so we're supposed to say something like "Half an apple are not enough for the salad"?