round to 3 significant digits

A pharmacist orders a shipment of four different types of cough medicine: 15 bottles of Brand A, 12 bottles of Brand B, 8 bottles of Brand C, and 5 bottles of Brand D. If 4 patients have a prescription for cough medicine, what is the probability that: a. each patient receives a different brand of cough medicine? Question 1 of 7 b. all 4 patients receive Brand A? Round to 3 significant digits. c. none of the patients receive Brand B or Brand D