How large must a group of people be in order to guarantee that there are at least two people in the group whose birthdays fall in the same month? a) 2 people
b) 3 people
c) 12 people
d) 13 people

d) 13 people

Explanation:

According to the Pigeonhole Principle, it states that given that several X commodities are placed into Y containers, and the number of X commodities is greater than the number of Y containers, then there will be a minimum of one Y container having more than one X commodities.

Hence, in this case, since the month is 12 in numbers, then to have at least two people in the group whose birthdays fall in the same month, the group must be at least 13 people.