1. Why in the world did she think you were pregnant? -I was sick a couple of times, and I guess she just put two and two together and made five.
2. When he saw the actor go to the actress's house alone at night, the journalist put two and two together and made five, claiming they were in a romantic relationship.

Also used with larger totals to suggest wilder or more exaggerated incorrectness: "put two and two together and make about five hundred".