※ 引述《orchety (silver lin)》之铭言： : 31. : A certain basket contains 10 apples, 7 of which are red and 3 of which are : green. If 3 different apples are to be selected at random from the basket, : what is the probability that 2 of the apples selected will be red and 1 will : be green? : 网路上看到的Answer好像是21/40 : 解释： : 2 red out of 7 gives 7c2 : 1 green out of 3 gives 3c1 : 3 apples out of 10 gives 10c3 : ncr = n!/r!(n-r)! : (7c2* 3c1)/ 10c3 = 21/40 : 我知道C是指『相异物』取n个不计顺序排列..可是这里是7颗红球长得都一样. : 3颗绿球也是相同物..有点难理解耶..哪位大侠好心解说一下呀~ : appreciate ~ 7/10 * 6/9 * 3/8 * 3 = 21/40 就把原本取物的机率乘以三就可以了（十颗苹果七个红的，九颗苹果六个红的....类推） 因为苹果拿出的顺序可以为红红绿 绿红红 红绿红三种可能 --

※ 发信站: 批踢踢实业坊(ptt.cc) ◆ From: 140.112.7.59 ※ 编辑: DanceDan 来自: 140.112.7.59 (10/26 20:20)