Could you please help me with question 4.48?

4.48 The CFO of a hospital is concerned about the risk of patients contracting an infection after a one-week or longer stay in the hospital. A long-term study estimates that the chance of contracting an infection after a one-week or longer stay in a hospital is 10%. A random sample of 50 patients who have been in the hospital at least 1 week is selected. a. If the 10% infection rate is correct, what is the probability that at least 5 patients out of the 50 will have an infection? b. What assumptions are you making in computing the probability in part (a)