A doctor is seeking an anti-depressant for a newly diagnosed patient. suppose that, of the available anti-depressant drugs, the probability that any particular drug will be effective for a particular patient is p = 0.4. what is the probability that the patient will need to
a. take 5 different drugs until the effective one is found.
b. take 6 different drugs until the effective one is found.
c. take 8 different drugs until the effective one is found.