作者ntnulcy (要活就要Don't)
看板Statistics
标题[问题] 掷骰子问题
时间Sun Nov 25 17:00:31 2007
Two fair eight-sided dice are rolled independently
(each is numbered from 1 to 8)
(a) What is the probability that neither one is 1 or 2 ?
(b) If the two faces are different, what is the probability that neither
one is 1 or 2 ?
我的想法：
(a)
设 P(E) = 第一次掷出1或2点骰子的机率
P(F) = 第二次掷出1或2点骰子的机率
所求为 P(E的补集∩F的补集)
= P(E∪F)补集 = 1 - P(E∪F)
又 P(E∪F) = P(E) + P(F) - P(E)P(F) (因为独立)
= 1/4 + 1/4 - (1/4)*(1/4) = 7/16
所求 = 1 - 7/16 = 9/16 #
(b) 骰子点数不同情况下，没有出现1或2的机会
6 * 5 30 15
= ──── = ── = ──
8 * 7 56 28 #
再麻烦一次大家帮我看一下 Orz
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1F：推 smilestupid:Yes 算出来结果一样 11/25 19:50