212. Patients in a study are tested for sleep apnea, one at a time, until a patient is found to have
this disease. Each patient independently has the same probability of having sleep apnea.
Let r represent the probability that at least four patients are tested.
Determine the probability that at least twelve patients are tested given that at least four
patients are tested.
(A)



答案:C
統計:A:0,B:0,C:0,D:0,E:0
難度:計算中