Smile 發問於 科學及數學數學 · 2 月前

Maths problem: i don't know how to do (c), it's so difficult, thanks?

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1 個解答

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  • 2 月前
    最愛解答

    (a)

    P(red) = x/48 = 1/16, so x = 48/16 = 3.

    P(yellow) = y/48 = 1/12, so y = 48/12 = 4.

    (b)

    The number of black balls is

    48 - x - y

    = 48 - 3 - 4

    = 41

    Therefore, P(black) = 41/48.

    (c)

    Let the required number be n.

    After taking out n black balls, there are (48 - n) balls in total where (41 - n) are black.

    Therefore,

    P(black) = (41 - n)/(48 - n) = 4/5

    5(41 - n) = 4(48 - n)

    205 - 5n = 192 - 4n

    5n - 4n = 205 - 192

    n = 13

    Thus, 13 black balls should be taken.

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