I am calculating the stream density S (= river length L divided by stream area A). The river has a length L of 671.8 +- 5.9 km and the stream area is 1860.2 +- 19.8 km^2. The stream density is thus and 0.36114396 km^-1 its error (calculated by the laws of error propagation by division) is 0.00498359 km^-1. What is the correct way to report this value and its uncertainty with respect to significant figures and/or digits after the decimal point? And why?
How should it be reported in the case of (100 +- 0.034) + (150 +- 0.2) = 250 +- 0.202869?
Thanks