Exam DEA-3TT2 topic 1 question 42 discussion

To calculate the MTBF (Mean Time Between Failures) of a system, we first need to determine the total operating hours in a week and the total hours of system failure within that week. Then, we divide the uptime by the number of failures. First, we calculate the operating hours: The system operates 24 hours a day from Monday to Saturday. There are 6 operating days in a week. Thus, the total operating time in a week is 24 hours/day * 6 days = 144 hours. Next, we calculate the total system failure time during the week: Tuesday: 5 A.M. to 7 A.M. (2 hours) Thursday: 4 P.M. to 8 P.M. (4 hours) Friday: 8 A.M. to 11 A.M. (3 hours) Sum of failure hours: 2 + 4 + 3 = 9 hours The total uptime in a week is 144 hours (total operating time) - 9 hours (failure time) = 135 hours. Finally, we calculate the MTBF by dividing the uptime by the number of failures: MTBF = 135 hours / 3 failures = 45 hours. Therefore, the correct answer is: C. 45 hours

is this not 45?