To find the mean time spent by each class, we add up all the times and divide by the number of students in each class.
For Class A:
(13 + 5 + 18 + 2 + 19 + 17 + 5 + 16 + 4) = 99
Mean time for Class A = 99 / 9 = 11 minutes
For Class B:
(9 + 19 + 11 + 9 + 16 + 2 + 14 + 8 + 2) = 90
Mean time for Class B = 90 / 9 = 10 minutes
The mean time Class A spent completing the quiz is 11 minutes.
The mean time Class B spent completing the quiz is 10 minutes.
The mean times Class A and Class B spent completing the quiz differ by 1 minute.