How many people are needed to guarantee that at least 4 people have a birthday in the same month?

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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**Question:**

How many people are needed to guarantee that at least 4 people have a birthday in the same month?

**Explanation:**

This question relates to the principles of the pigeonhole problem in probability and combinatorics. To ensure that at least 4 people share the same birthday month, we consider the worst-case scenario:

There are 12 months in a year. If we distribute people across these months and want to guarantee that at least one month will have at least 4 people, we use the formula:

\[ n = 12 \times (k-1) + 1 \]

where \( k \) is the number of people we want in the same month (in this case, 4). Therefore:

\[ n = 12 \times (4-1) + 1 \]
\[ n = 12 \times 3 + 1 = 37 \]

So, 37 people are needed to guarantee that at least 4 people have a birthday in the same month.
Transcribed Image Text:**Question:** How many people are needed to guarantee that at least 4 people have a birthday in the same month? **Explanation:** This question relates to the principles of the pigeonhole problem in probability and combinatorics. To ensure that at least 4 people share the same birthday month, we consider the worst-case scenario: There are 12 months in a year. If we distribute people across these months and want to guarantee that at least one month will have at least 4 people, we use the formula: \[ n = 12 \times (k-1) + 1 \] where \( k \) is the number of people we want in the same month (in this case, 4). Therefore: \[ n = 12 \times (4-1) + 1 \] \[ n = 12 \times 3 + 1 = 37 \] So, 37 people are needed to guarantee that at least 4 people have a birthday in the same month.
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