Problem 1267. Calculate the probability that at least two people in a group share the same birthday.

Created by Jeremy

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Calculate the probability that at least two people in a group share the same birthday. Given an integer input n, return to 0.015 (1.5%) precision the probability of this being the case. Assume that every day is equally probable as a birthday and ignore the leap year.

Example:

Input: 1
Output: 0.00

Input: 366
Output: 1.00

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Last Solution submitted on Dec 22, 2025

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Massimo Zanetti on 7 Oct 2016

I assume n is the number of people in the room.....

Edward Huang on 5 Mar 2020

Although I got the solution, in the case of n=100, however, it results in 1.000, which means there MUST be at least two people share their birthday in a group of 100. Am I missing something here?

Marco Riani on 8 Mar 2025

In case n=100 the exact probability is 0.999999692751072 therefore it could happen (although it is very unlikely) that no one shares the same birthday

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Problem 1267. Calculate the probability that at least two people in a group share the same birthday.

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Problem 1267. Calculate the probability that at least two people in a group share the same birthday.

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Last 200 Solutions

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