Times for a surgical procedure are normally distributedMethod A has a mean of 28 minutes and a standard deviation of 4 minutes for completion. (a) What is the probability that a surgical procedure conducted by method A takes at least 31 minutes to complete ? Draw a graph to illustrate your results . b) Suppose you conducted the surgical procedure (using method A) on a sample of patients. With the probability of 20%, the average time of completion for the surgical procedure under Method A will be at most how many minutes? Draw a graph to illustrate your results