Luke Skywalker: Hmmm in this things i'm almost always correct...........:-)
But as i see now i'm not correct or incorrect as NIST hasn't defined clearly what is happening with "prefix"-units.

So from http://physics.nist.gov/Pubs/SP811/sec09.html#9.7 :
"A derived unit is usually singular in English"

And from http://physics.nist.gov/cuu/Units/units.html :
we see that centimetre it's not a base unit, but not a derived one too, it's a "prefix"-unit if we can say that.

So what ist's the final judgement......?


Walter:
I don't said that because you have used "and" instead of "+" but because you hadn't used ( ) between the numbers.
It's wrong to say this is 5 and 1/2 meter tall.
The correct is (5 and 1/2) meter tall.
Because in the first case the meter goes to the 1/2 ONLY while 5 remains a single number and not a unit of length.........