Final answer:
The probability that a phone call lasts between seven and nine minutes is 3/8. The average duration of the phone calls is 2.88 minutes per call.
Step-by-step explanation:
The list of durations for Sam's phone calls is {9, 15, 5, 7, 9, 12, 11, 4}. To find the probability that a phone call lasts between seven and nine minutes, we need to count the number of phone calls that fall within that range and divide it by the total number of phone calls. In this case, there are 3 phone calls that last between seven and nine minutes (7, 9, and 9), so the probability is 3/8.
If 25 phone calls are made one after another, we can calculate the average duration by finding the total duration of all the calls and dividing it by the number of calls. The total duration of the calls is 9+15+5+7+9+12+11+4 = 72 minutes. Therefore, the average duration is 72 minutes / 25 calls = 2.88 minutes per call.