Site 2 times in top ten with same keyword.

Hi,

My website was this week in google on # 5 and #6
The main page was on #6 and a subpage was on # 5

So the sub site ranking better then the main site on same keyword.

What happend today is that the main site droped to # 29 and the subsite is stil on # 5

I do not understand how this works and why the main site drops to #29.

If someone could explain this to me would be nice.

Thanks for reading and for your time to share your info.

Regards

Thanks a lot for helping.

Martin