A quality control manager uses test equipment to detect defective computer modems. A sample of 3 different

Question:

A quality control manager uses test equipment to detect defective computer modems. A sample of 3 different modems is to be randomly selected from a group consisting of 12 that are defective and 18 that have no defects. What is the probability that (a) all 3 selected modems are defective, and (b) at least 1 selected modem is defective?