Saturday, April 18, 2009

Happy birthday, Bill and Barbara


Today is their birthday. Bill and Barbara have the same birthday.
I don't know how old they are. If they were born on the same day and year, they are twins? They do look alike.

In probability theory, the birthday problem, or birthday paradox[1] pertains to the probability that in a set of randomly chosen people some pair of them will have the same birthday. In a group of at least 23 randomly chosen people, there is more than 50% probability that some pair of them will both have been born on the same day. For 57 or more people, the probability is more than 99%, and it reaches 100% when the number of people reaches 367 (there are a maximum of 366 possible birthdays). The mathematics behind this problem leads to a well-known cryptographic attack called the birthday attack.

2 comments:

  1. Charles;
    How many people at least needed who had same birthday?

    You gave me this question befoere?
    Right?

    ReplyDelete
  2. This has got to be a Charlie question. Maybe Judge Judy can help Charlie.

    ReplyDelete