What is the probability that at least 2 people in a random group of 4 people have a birthday on the same day of the week? Answer:

Answer 1

The opposite event is that 4 people have
birthdays on different days of the week.
Its probability=(7*6*5*4)/(7^4)=120/343
Therefore, P=1-120/343

Answer 2

sum(dbinom(2:4,4,1/7)) = 0.1003748