c**********e
发帖数: 2007 | 1 Let r be a fixed positive integer, and let W be the waiting time until the
r-th head in a sequence of fair coin tosses. Find simple formula in terms
of r for the median of W, that is, the least integer w so that P(W>w)<=1/2. | c******s
发帖数: 270 | | c**********s
发帖数: 295 | 3 w=2r-1
w is the same for r-head and r-tail | c********k
发帖数: 24 | 4 这个watiting time是不是出现r次head之时总共throw的次数?
你是怎么得到这个答案的呢?
【在 c**********s 的大作中提到】
: w=2r-1
: w is the same for r-head and r-tail
| c**********s
发帖数: 295 | 5 say you throw 2r times, it is easy to show P(H>=r)>1/2
and it is easy to prove this is not true for 2r-1 since P(H>=r)=P(T>=r) |
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