Odd Number of Matchs

I'm doing some research-based on the number of results returned by a bing search.
I recently noticed when I use the same term 2 times on the query I get more results than a search for the term a single time.
For example, searching for "car", bing returns 79,600,000 but when I search for "car car" I get 2,870,000,000.

Can anyone explain this behavior?

Thank you in advance :)