Equations and inline and display! Need some help

[Mithos]

Hi guys,



I have a statistics assignment and I want to put every formula into a word file. It's working pretty good however I have some problems with the sum symbol. Take a look at the screen below. The top formula is correct however I want the n and the i=1 above and below the sum symbol like you see in the bottom formula. The top formula is inline and the bottom formula is display. However when the formula is in display it is impossible for me to get "Xj =" so I am forced to use inline however the sum symbol doesn't look like it should look.

I hope you get my problem and I hope that there is a solution. Would be awesome

EDIT:
Got another question now I try in display mode to add the sum symbol in an equation however I again get a small sum symbol as seen in picture 2. How do i get it like on the photo?