1. The problem statement, all variables and given/known data Consider a measure f mapping from a family of sets A to [0,infinity] Let the measure be finitely additive and countable subadditive. Prove that f is countably additive on A. 3. The attempt at a solution To show equality from an inequality we do ie. a<=b>=a so a=b I tried this strategy with measures and sets but couldn't see it through. I might need to construct another set but don't see what to construct.