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Math Help - Binomial Propability

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    Binomial Propability

    During winter it rains on average 18 out of 30 days. Five winter days are selected at random. Find correct probability that:

    a) First two days choosen will be fine and the remainder wet.

    I attempted 5C2 (12/30)^2 (18/30)^3 counting exactly 2 days fine and 3 days rain.

    Then i calculated probability first 2 days raining, which is (2!/2!3!)/5!/(2!3!) = (2!x3!x2!)/5!

    to attain 0.06912 which is not same as answer. Where did i go wrong?
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    Quote Originally Posted by Lukybear View Post
    During winter it rains on average 18 out of 30 days. Five winter days are selected at random. Find correct probability that:

    a) First two days choosen will be fine and the remainder wet.

    I attempted 5C2 (12/30)^2 (18/30)^3 counting exactly 2 days fine and 3 days rain.

    Then i calculated probability first 2 days raining, which is (2!/2!3!)/5!/(2!3!) = (2!x3!x2!)/5!

    to attain 0.06912 which is not same as answer. Where did i go wrong?
    The order matters:

    (18/30)^2 (1 - 18/30)^3
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