Answer
$P(E)=\frac{7}{365}\approx0.0192$.
It means that, if we randomly select 3650 people, we would expect that the number of people that have a birthday on the 31st day of a month is about 70.
Work Step by Step
Event = "birthday on the 31st day of a month" = {Jan 31, Mar 31, May 31, Jul 31, Aug 31, Oct 31, Dec 31}. So, $N(E)=7$
One year = 365 days, so $N(S)=365$
Using the Classical Method:
$P(E)=\frac{N(E)}{N(S)}=\frac{7}{365}\approx0.0192$
