The Birthday Problem

Given that everyone’s birthday is absolutely random, how many people
must be in the room such that there is more than even chance (at least
50%) that

• Another person would have the same birthday as you (ANS: 365/2 =
  183 persons)
• Two persons would have the same birthday (ANS: 23 persons)

The difference is that you fix the date in the former. But you let the date vary in the latter. It is obvious that you would need less people in the latter than in the former. But the surprising result is that it is a lot less.


This result can explain few strange and embarrassing incidents. Canadian lottery officials planned to awards cars to five people who own winning lottery tickets. The system ended up generating the same number twice. The person who has that number won two cars.

Given the number of the first winning lottery, the chance that the second lottery will repeat the first one can be made very slim. However, the chance that two winning tickets are the same is not.

Source: The Drunkard's Walk: How Randomness Rules Our Lives by Leonard Mlodinow, Chapter 3 [Read the Book Review] [Read the Previous Part] [Read the Next Part].

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Book or Audiobooks?

Personally, I prefer audiobooks. It's fun, and I can listen when I'm doing something else. It also makes other activities (e.g., jogging) a lot more fun. For more detail about audiobooks, please read [this post].

There is one more reason that may encourage you to go for the audiobook version. You can get it now for FREE. Audible offers you a free trial for 14 days. Even if you get the book and cancel the subscription right away (so that you don't have to pay), you can keep the book. And, don't worry if you lost the audiobook file. Just log into audible.com. You can keep downloading the over and over again.


About the summary: It takes time to finish up a book. And, when you do, sometimes, you want to review what you learn from the book. If you do not make notes as you read, you might have to go through the book once again. This can be time-consuming when you are dealing with a book. But you can still flip through the book and locate what you are looking for

However, when the material is an audiobook, it is extremely hard to locate a specific part of content. Most likely you will have to listen to the entire audiobook once again.

This book summary will help solve the pain of having to go through the book all over again.

I am leaving out the details of the books. Most books have interesting examples and case studies, not included here. Reading the original book would be much more entertaining and enlightening. If you like the summary, you may want to get the original from the source below.