i noticed that i've been getting this type of question consistently wrong, in the new sat prep. i'm not sure what kind of problem it exactly is either, so i could not find an explanation. i would really appreciate it if you could explain this whole concept, if that's possible? thank you so much!
(1/x) + (4/x) = (1/72)
Cities and towns use water treatment facilities to remove contaminants from surface water and groundwater. Suppose a town has a treatment plant but decides to build a second, more efficient facility. New treatment plants can filter the water in the reservoir four times as quickly as the older facility. Working together, the two facilities can filter all the water in the reservoir in 72 hours. The equation above represents the scenario. Which of the following describes what the term (1/x) represents?
I think you did not give the choices at the end. But it looks as if 1/x represents the fraction of the reservoir that the older facility can filter in one hour. (Together the two facilities fill 1/72 of the reservoir in one hour).