FILE No.64Unsolved
The culprit is someone at a party. The only clue: "the culprit shares a birth month with someone else."
The guest list gives only the number of guests, not their birth months. The detective wants to know how many guests are needed so that someone must share a birth month with another.
There are 12 birth months, January to December.
What is the smallest number of people that guarantees two or more share a birth month?
If you get stuck, open the hints one at a time, in order.
Can 12 people all have different birth months?
What happens when one more person arrives?
Look for the smallest number that guarantees a match.
What is the smallest number of people that guarantees two or more share a birth month?
Choose the answer closest to the truth.
13
The answer is: 13.
With 12 people, everyone could have a different month (one per month), so 12 does not guarantee a match. With 13 people, at least two must share one of the 12 months. This is called the pigeonhole principle: 13 pigeons in 12 holes means some hole holds two.
People answer 12, the same as the number of months.
The cases on this site are fictional puzzles created for entertainment. Any resemblance to real people, organizations or events is coincidental.
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