Question 434207
We can assume that everyone must have between 0 and, say, 999,999 hairs. With an arbitrarily large population, there must be at least two people with the same number due to the Pigeonhole principle.


There are 26 letters for the last initial. If there are at least 79 people (3*26 + 1), then by the Pigeonhole principle, there must exist four people with the same last initial.