How much content needs to change to avoid duplicate content?

Selected answers from the Dumb SEO Questions Facebook & G+ community.

• 
  Lyndon NA: Duplicate content is content that is identical or highly similar.If G see`s 2 or more pages that are identical/highly similar - it will select 1 to show, and not show the other in the SERPs ...... for terms that pertain to the duplicated content.Example :Page 1 : A B C D E F G H H H H Page 2 : Z Y X W V U T H H H HIf I search for "B D E", I will see Page 1 in the SERPsIf I search for "W V U" or "Z Y X", I will see Page 2 in the SERPsIf I search for "H H H", I will only see Page 1 or Page 2 - Google will not show me both Page 1 and Page 2 in the SERPs.Identical/Mostly Identical pages also have the problem of being canonicalised - G may decide they are technically the same page, in which case it may decide to only show 1 page - but you generally have to have identical/incredibly similar pages for that to occur.So - how similar are the pages?30%? 50%? 80%?If the degree of similarity is high or higher (say 60%+ of the pages are the same), then you may want to alter your approach.Put the message in a separate page, then load it in to other pages via an frame/iframe.(Do NOT set the message page as "noindex", or block it with robots.txt!)
• 
  Greg Kristan: If it is just a message, I would recommend putting that into an I-frame so Google won`t see it.