thank you for attention and patience. Every piece of advice is very helpful to me as it teaches me of the usefulness of maple. But I wasn't honest with you. What I must really count is this little monster: int((sum((x[i]-b)*exp((x[i]-b)^2/(2*sigma^2)), i = 1 .. k)-(sum((y[j]-b)*exp((y[j]-b)^2/(2*sigma^2)), j = 1 .. n)))^2, b = c .. d) I tried to solve it with a leaf of paper and my head but obviously I'm too stupid. I need a formula for further computation. I tried modifying your code then find a nice short formula to simplify the result but I not able to deal with this too. Have anyone an idea how to attack my problem :/ I have nobody else to ask :(. Once more thank you. This is a very nice forum.

thank you for fast reply. I read help files but i don't find suitable solution for me. I sum random variables x_i, y_j so i think it's hard to write this equation with maple Sum that seems to be more appropriate for polynomials or series. I think I would need an array and a for loop. Later I want to count integral of this expression of variable b. I can't solve my problem on my own :/.