302.05 grams
There are 4 significant digits
All four of them.
3 of them.
302.05 grams
5
4 of them.
five. 30.002
10.1+25.01+5.08
The rule when rounding off numbers is "If the first figure to be discarded is 5 or more then the previous figure is increased by 1". When 16490 is rounded off to 2 significant figures then the first figure to be discarded is 4. As this is less than 5 then the previous figure (6) is not increased by 1. 16490 to 2 significant figures is 16000.
I would use grams because grams would give you more significant figures for the measurement than kilograms
1.0 gram has 2 significant numbers while the 1 gram only has 1. This means that the 1.0 gram is measured more accurately. For cooking, yes, its the same. For synthesis of chemicals, no, its not.