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Math Help - Maths & Statistics question; probability.

  1. #1
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    Maths & Statistics question; probability.

    In a class of 33 boys and 8 girls what is the probability of the first and second child to arrive in the morning to be a boy?

    Thanks in advance to anybody who answers
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  2. #2
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    P(boy) = \frac{33}{41}

    The probability of first two children being boys is \frac{33}{41} \times \frac{33}{41}\, assuming each child arrives independently.
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  3. #3
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    Quote Originally Posted by nzmathman View Post
    P(boy) = \frac{33}{41}

    The probability of first two children being boys is \frac{33}{41} \times \frac{33}{41}\, assuming each child arrives independently.
    Hey, thanks for taking the time to reply.

    I am not big on Maths, and am doing this as a small part of my Sociology course (Statistics), but the answer you gave is exactly the same answer that I gave, 33/41. I thought it might be wrong when I wrote it but wanted to write something rather than nothing.

    It is marked wrong. So are we sure that is the right answer?
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  4. #4
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    I said \frac{33}{41} \times \frac{33}{41} is the answer,

    ie \left(\frac{33}{41}\right)^2
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  5. #5
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    Quote Originally Posted by JohnT View Post
    In a class of 33 boys and 8 girls what is the probability of the first and second child to arrive in the morning to be a boy?

    Thanks in advance to anybody who answers
    If you draw a tree diagram it should be clear that the answer is \left(\frac{33}{41}\right) \cdot \left(\frac{32}{40}\right).

    Quote Originally Posted by nzmathman View Post
    I said \frac{33}{41} \times \frac{33}{41} is the answer,

    ie \left(\frac{33}{41}\right)^2
    This answer will only be correct if the first child goes back home because s/he forgot his/her lunch .....

    (In other words, sampling with replacement)
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  6. #6
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    Oops, sorry about that mistake, should have realised there was no replacement
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  7. #7
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    Looks like I got a clone lol
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