To reduce testing costs, blood tests are conducted on a pooled sample of blood collected from a group of n people. If the test is negative in the pooled blood sample, none have the disease. If the test is positive, the blood of each individual must be tested. The individual tests are conducted in sequence. If, among a group of four people, one person has the disease, what is the probability that five blood tests (including the pooled test) are required to detect the single diseased person?