请问这题 There are k+1 coins in a box. The ith coin will,when flipped,turn up head withprobability i/k ,i=0,1,...,k . A coin is randomly slected from the box and is then repeatedly filpped. If the first n flips all results in heads, what is the conditional probability that the (n+1)st flip will do likewise? 答案写 P((n+1)st head | n次head) 1 1 2 k-1 k k+1 =--(--+--+.....+---+--)=---- k k k k k 2k ^^ 可是不懂第一项 1/k怎麽来的@@ 请问谁会呢? --

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