pages is gone

My macbook pro is a 2011 model. And it came with iwork on it, including pages. Its been updated to Yosemite. Except that now, pages, and all of iwork is gone. And I know I didn't uninstall them. Also I still have .pages documents on my machine that I can open, but only with Preview.

I really don't understand what happened. But I do not want to pay to have to replace these apps when they came with machine for free in the first place and had been updated. Is there anyway to get them back? Why did they disappear in the first place.

I did a factory rest not long ago when I got a new imac and wanted to clean this up. And Iwork was there. But somewhere in the process of updating this machine to Yosemite, iwork and its apps have now been removed from my machine, but .pages documents I had are still present but now can only be opened with preview as image files.