If I have a standard deviation and mean for one distribution center, but I have to find it for 5 of the same type of dist center with the same SD and mean how do I do that? Solution The formula is ^2(x+y) = ^2x +^2y So you add the variances (squares of standard deviation) of the five centers together and you will have the variance of the sum of all of them. Then take the square root of that to get the standard deviation..