If we are measuring the length of bugs. (let's say they are either green color or red color), and the bugs are stratified based on two colors. We know the mean and variance within the two subpopulationsseparately ( we can get two sampling distributions of mean for the two subpopulations). Then, if we take asample from the overall population, how do we get the mean and variance for the sample mean? (does it depend on the prevalence of color?)