One hundred people each with either all white hair or all black hair are arbitrarily seated in four rooms. Then the most significant number of people with the same colour hair we can be sure of finding in at least one of these rooms is
I know we should use the pigeonhole principle,
if I consider 50 people with black hair and 50 people with white hair, I take 50 people(of either all black or all white hair) and there are 4 rooms
so I do $\lceil 50/4 \rceil = 13$
is it the correct way?