I've got two sets of data from some fluorescent cells.
The first set is when the cells don't have their fluorescence switched on, but they are still faintly glowing.
The second set is when they do have their fluorescence switched on.
I ran each of the two experiments three times, so n=3, and I therefore have a mean for each dataset and a SD.
I need to subtract the non-switched on set from the switched on set in order to determine the amount of fluorescence that arises as a result of being switched on.
How do I then calculate the SD of the final value?
I know that for discrete random variables,
$$ E[X+Y] = E[X] + E[Y] $$
So I assume that holds true for subtraction as well, but I can't find the rules for continuous random variables, as these are.
Example data for one data point:
ON OFF MEAN: 33956.6666 3835.66667 SD: 457.47301 38.0905