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Hi everybody, first reply for me, here. Linux and math fan, so: about the 'birthday' question of the Cambridge test, here is my modest explanation: If we have 3 guests, ...
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  1. #11
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    Hi everybody,

    first reply for me, here. Linux and math fan, so:
    about the 'birthday' question of the Cambridge test, here is my modest explanation:
    If we have 3 guests, the probability that a fourth one has another birthday than the 3 others is P:
    prob that she is not born the same day than the first: 364/365
    and that she is not born the same day than the second: 363/365
    and that she is not born the same day than the third: 362/365
    simultaneously, so: P =364/365 * 363/365 * 362/365
    The probability this fourth one has the same birthday as one
    of the 3 others is, complementary: 1-P
    If we have n guests, P =364/365 * 363/365* ... * (366-n)/365
    Now we have to find n as 1-P >= 1/2 or P <= 1/2
    5 lines of Python code give n =23 (1-P =0.507..)

    Enjoy

  2. #12
    Just Joined! Peter D's Avatar
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    I have an issue with the question about the die. The question says that the die has the numbers to 6 on each side. I take that to mean that each side has the numbers 1 to 6. Therefore you will get the number six on every throw of the die. I'm sure that's not what they meant but if you ask a stupid question you get a stupid answer. The language used in one or two of the other questions was imprecise.

  3. #13
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    Quote Originally Posted by Peter D View Post
    I have an issue with the question about the die. The question says that the die has the numbers to 6 on each side. I take that to mean that each side has the numbers 1 to 6. Therefore you will get the number six on every throw of the die. I'm sure that's not what they meant but if you ask a stupid question you get a stupid answer. The language used in one or two of the other questions was imprecise.
    you are perfectly right, we have to invoke the common sense to see the problem. This could be " each face of an unbiased cube are numbered from 1 to 6, .." The question is a bit questionable too. Anyway, the probability theory tells us 6

    cheers

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  5. #14
    Linux Engineer MASONTX's Avatar
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    Quote Originally Posted by henri0331 View Post
    you are perfectly right, we have to invoke the common sense to see the problem. This could be " each face of an unbiased cube are numbered from 1 to 6, .." The question is a bit questionable too. Anyway, the probability theory tells us 6

    cheers
    Depends on the wording of the question. If one person rolls the dice infinite amount of times, the average number of rolls between 6's will be 6. If you take infinite number of people and have them roll until they get a 6, the average number of rolls wil be 3.5, 1/6th of the people getting a 6 in 1 roll, 1/6th in 2 rolls etc. Only 1/6th of the people would require 6 rolls to get a 6.
    Registered Linux user #526930

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