Finnegan Pharma has reported that a certain form of its tuberculosis skin test has experienced substantial false-positive and false negative results recently. In a region experiencing an outbreak of this infectious disease, 80% of patients experiencing symptoms and were screened with the Finnegan Pharma skin test administered by medical professionals were noted as testing positive for tuberculosis. However, more comprehensive clinical testing with blood work has shown that, of these patients presenting symptoms and initally diagnosed with tuberculosis, only 60% actually had the infection, a true positive result. Of those who did not test positive with the initial skin test, 75% also tested negative when fully screened with blood work, a true-negative result. [COMMENTS & HINTS: Draw a tree diagram to sort out the information and guide your calculations.]

#7: What is the compound probability that a patient presenting with symptoms of tuberculosis both initally tests negative with a skin test and then also tests negative when fully screened with blood work? This compound probability computes the likelihood of a true negative outcome. [COMMENTS & HINTS: [Enter the answer as a whole percentage. You should include the percentage symbol.]