匿名
匿名 發問於 教育及參考書小學及中學教育 · 9 年前

probability

there are 8 poles along one side of a street.8 different flags are hoisted in random order such that each pole have a flag hoisted on it.let e be the event that 3 particular flags are next to each other and f be the event that any 2 of the 3 particular flags are not next to each other

1.find p(e) and p(f)

2.are e and f complementary events?why

1 個解答

評分
  • 9 年前
    最愛解答

    1)3 particular flags as a unit , there are 3P3 ways for this unit , total 6 units with other 5 flags.p(e)

    = 3P3 * 6P6 / 8P8

    = 6 * 720 / 40320

    = 3/28

    Let other 5 flags be A , B , C , D , E : 5P5 ways ( ) A ( ) B ( ) C ( ) D ( ) E ( )Put 3 particular flags to 3 ( ) among 6 : 6P3 ways All ways for 3 particular flags and 5 flags : 8P8 ways p(f)

    = 5P5 * 6P3 / 8P8

    = 120 * 120 / 40320

    = 5/14

    2)No.Because of exist the case : The 1st and the 2nd particular flags are next to each other but the 3rd are not.

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