The Martian calendar has sixteen months instead of twelve Wh

The Martian calendar has sixteen months instead of twelve. What is the fewest number of Martians so that five of them will have the same birth-month?

Solution

The martian calendar has sixteen moths.

Lets say 16 different people are there -> 16

To make all the people have same month -> 16*5 = 80

The fewest number of Martians, so that five of them will have the same birth-month -> 80 - 15 -> 65