Question about Calories on pre-packaged foods

ok, so I just had some sushi with the following nutrition facts..

15g fat, 75 grams carbohydrates, 10g proteins and they list the total amount of calories to be 390.

I'm not mistaken that 1g carbs= 4 calories, 1g protein= 4 calories & 1g fat= 9 calories..correct?

Well I did the math on the sushi and (15*9)+(75*4)+(10*4) = 475!! not 390?

What's the deal? Can they really get away with being that off on their math? And this isn't just some shrinky dink little company, it's a fairly widespread brand of sushi.

What's the deal?

Was part of the carbohydrate fiber?  I don't think that fiber has 4 calories per gram, since it is "indigestible".

aha! 6 grams of fiber. so that explains 24 calories of it, but that still leaves about 70 mystery calories..whats the deal?

It'll be a rounding error.  There are not precisely 9 calories in a gramme of fat, for example but probably 9 point something...

oh ok I guess that would make sense. Kind of annoying though, it would be so nice if everything was perfectly numbered! :) Thanks gi-jane.