probability

[匿名]

2012-02-18 2:34 am

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

回答 (1)

用戶2053

2012-02-18 8:19 pm

✔ 最佳答案

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.

👍 0 👎 0