Nana has a water purifier that filters 1/3 of the contaminates each hour

[10 points, algebra 2]according to my answer key the restrictions are -1 and 4. but why not positive 1?

Abacteria population is tripling every hour. by what factor does the population change in 1/2 hour? select all that apply

Aye asap pls ! markin da brainiest too ! btw da step choices are all add, distribute, divide, n subtract