What's the probability that a student with a black tongue depressor has Diseasitis? From the diagram, there are 18 sick students with black tongue depressors\. 18 \+ 24 = 42 students in total turned their tongue depressors black\. Imagine reaching into a bag of all the students with black tongue depressors, and pulling out one of those students at random; what's the chance a student like that is sick?

Is this the same question as : what is the probablity that the test gives correct results ? We can also ask 3 other questions :

- What is the probability of a student with a black tongue depressor do not have Diseasitis ?
- What is the probability of a student witiout a black tongue depressor have Diseasitis ?
- What is the probability of a student witiout a black tongue depressor do not have Diseasitis ?