premise: Newington is a census-designated place (CDP) in Fairfax County, Virginia, United States. The population was 12,943 at the 2010 census. The 2010 census showed a significant decrease after half the population was split off to the newly created Newington Forest CDP.
hypothesis: Before the population was half way split to the Newington Forest CDP, it was higher.
reason: It is definitely correct because the context states that it decreased "after" it was split off, so logic tells us that "before" it split, it was higher. The computer cannot use this type of logic yet so it was unsure. 