This problem is isomorphic to: "20% of the patients in a screening population have Diseasitis\. 90% of the patients with Diseasitis turn the tongue depressor black, and 30% of the patients without Diseasitis turn the tongue depressor black\. How many patients that turn the tongue depressor black have Diseasitis?"
I think isomorphic is too advanced vocabulary to be assumed for Math 1. Would this be a good opportunity to use a popover with the definition?