6. A new study is being planned to test the effectiveness of a new vaccine for HIV. The study enrolled 100,000 people with high risk of exposure to HIV. Everyone was screened for HIV as a part of the enrollment process and 128 people tested positive for HIV. The remaining people were randomized. 38,678 were placed into Study Arm A, which received the vaccine. The remaining 61,194 were placed Study Arm B, which received a placebo of saline. The group was followed for 1 year. At the 1 year follow up, 4,178 people in Study Arm A tested positive for HIV and 12,428 in Study Arm B tested positive. a. What is the prevalence of HIV at enrollment