Probability is the ratio of the number of possible outcome to the number of total outcome.
Given that for the past 60 days, on 39 of those days she arrived at work before 8 AM while for the rest of those days she arrived after 8:30 AM, the probability that she will arrive at 8 AM on the next day she goes to work
= 39/60
= 13/20
In decimal, this will be expressed as 0.65 and 65% in percentage.
