2) A flu outbreak occurred in a military barracks that housed 20 soldiers. Case A began on October 1 and case B was diagnosed on October 2. After approximately 10 days, 12 additional cases occurred during approximately a one-week time span. Military epidemiologists believed that this second group of cases represented the same generation of cases, and was in the second incubation period after the occurrence of cases A and B; none of the 20 soldiers was known to be immune. Calculate the secondary attack rate using the foregoing data.