During addition or subtraction, numbers in scientific notation need to be converted into the standard notation first. For example, 3.00 x 10^-4 is 0.000300 and 5.00 x 10^-3 is 0.00500. The result of addition, 0.000300 + 0.00500 = 0.00530 rounded to the fifth decimal place, same as 0.00500. In scientific notation 0.00530 is 5.30 x 10^-3.