A routine examination discovers a lump in a female patient’s breast. Only 1 out of 100 such lumps turns out to be malignant, but, to be safe, the doctor orders a mammogram X-ray test. If the lump is malignant, there is a 0.80 probability that the mammogram reading will be positive; if the lump is benign, there is a 0.90 probability that the reading will be negative. The test comes back positive and the doctor orders a second test, which comes back negative. Assuming the test results to be independent, what is your estimate of the probability that this lump is malignant?