When competing for the same ad unit, if the Ad Rank of a cost-per-thousand impressions (CPM), placement-targeted ad is higher than the combined Ad Rank of all competing keyword-targeted ads, then the:
- keyword-targeted ad will be the only ad to appear in the ad unit
- keyword-targeted ad will appear above the placement-targeted ad
- placement-targeted ad will be the only ad to appear in the ad unit
- placement-targeted ad will appear above the keyword-targeted ad
Explanation: Placement-targeted ads and keyword-targeted ads compete to appear on pages on the Display Network based on their Ad Rank. Ad Rank for placement-targeted or keyword-targeted ads, as well as all other ads targeted to the Display Network, is determined depending on whether the campaign uses cost-per-click (CPC) or cost-per-thousand impressions (CPM) bidding.
Read more here: https://support.google.com/adwords/answer/2580292?hl=en