The number of people that must be selected to make sure that there are at least 20 who are born in the same month is; n = 240 people
This question would be solved by application of the pigeonhole principle.
The pigeon hole principle states that for m = 12 months, if there are n ≥ 13 people in a group, then it is guaranteed that there would be a month in which at least two people's birthdays will occur.
This principle can be further stated as; if n = km + 1 objects are distributed among m sets, then at least on of the sets will contain at least k + 1 objects.
We are told that there are at least 20 people born in the same month. Thus k = 20.
Applying our formula gives;
n = 20m + 1
From the principle, m = 12.
Thus;
n = 20(12) + 1
n = 241 people
In conclusion, there must be 241 people selected for there to be at least 20 who are born in the same month.
Read more about pigeonhole principle at; https://brainly.com/textbook-solutions/q-6-state-pigeonhole-principle-4
