For example, the particle size distribution in two containers are (M1, SD1) and (M2,SD2) and both are mixing to a third container, what would be the mean, standard deviation of the mixer in third container.

Similarly, if two systems are in series, how can I find the resultant of these two distribution. For ex, there are two crushing mill, both have a crushing size distribution. From first crusher material goes to second one. How can I find the distribution of final output.

Thanks