for symptom-free women aged 40 to 50 who participate in screening using mammography, the following information is available for this region. the probability that one of these women has breast cancer is 0.8%. if a woman has breast cancer, the probability is 90% that she will have a positive mammography test. if a woman does not have breast cancer, the probability is 7% that she will still have a positive mammography test. what is the probability that a woman with a positive test actually has breast cancer?