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Melon
Lv 4
Melon asked in Science & MathematicsMathematics · 8 years ago

Binomial distribution homework question?

I made the stupid decision of sleeping in class, so now I have no idea how to do binomial distributions in word problems.

Here's the question:

"An ordinary fair cubical die is thrown 10 times. Given that there are at least 3 threes, fit the probability that the number of threes is 4 or more."

The answer, according to the answer key, is 0.3102.

So does anyone know the steps to getting that?

Thanks!

1 Answer

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  • M3
    Lv 7
    8 years ago
    Favourite answer

    hi melon !

    here's a quote from Albert Camus

    "Some people talk in their sleep. Lecturers talk while others sleep"

    It'd be better for you to talk in your sleep !

    to come to the problem

    just 1 way of getting a 3, 5 ways of getting a non-3

    so ways to get three 3's and 7 non-3's = C(10,3)*5^7 = 9375000

    ways to get 4 or more 3's

    = (sum of C(10,k)*5^(10-k), k = 4 to 10 ) = 4216176

    Pr = 4216176/(9375000+4216176) = 0.3102 <------

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