dulusementara

I've writed an equation of summation using equation of microsoft word 2007. When I tried (the first case) writing latex "\sum_(i=1)^n x_i ", the result is the summation with its limits at above and below the summation equation; but when i tried (the second case) writing latex "\sum_(i=1)^n x_i / n", the result is the summation with its limits at the side of the summation equation. The questions are: 1) how to make the summation limits in the second case still in the above and below? 2) for the first case, is there any latex commands that can allow the summation limits at the side of the summation? thank you. i also attach picture for the results of the first case and second case.