Supposed that a school bus, on the average, arrives at a particular bus stop at 8:30 am. However, as a statistics class project, actual times of arrival were recorded for a period of one semester. The students found that the bus arrival time has a standard deviation of 5 minutes. Given these data:

a. About what are the chances that the bus will arrive at 8:32 a.m. or later on any particular day?

b. Find the approximate probability that the average arrival time for a two-month period in which the bus comes 25 times is between 8:29 and 8:31 am.