Among patients with Diseasitis, 90% turn the tongue depressor black\. However, the tongue depressor is not perfect, and also turns black 30% of the time for healthy students\.
Another interesting question to ask is what is the single probablity of the tongue depressor to give accurate results ?
If we know that the tongue depressor has a 5% error on all students, sicks and non sicks, we can predict that the probability of being sick is (another rule here ? or another fashion of using the rule if applicable)