[商管] [數統] 98政大統研
數理統計的第4題=第3頁的4.(1)
http://small.lib.nccu.edu.tw/exam/data/master/sta/sta98.pdf
4.Let X be the number of independent trials of some component until it fails,
where 1-p is the probability of failure on each trial. We record the exact
number of trials Y=X, if X小於等於r; otherwise we record Y=r+1, where r is
a fixed positive integer.
(1) Give the discrete pdf of Y, f(y;p). show your work.
郭胖的解答寫
當y=1,2,..,r 則f(y)=p*(1-p)^(y-1)
y=r+1 則f(r+1)=P(Y=r+1)=P(X大於等於r+1)=(1-p)^r
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y不是直到第一次失敗所需試行次數嗎@@?
從這句 where 1-p is the probability of failure on each trial
得到每次試行中失敗機率=(1-p)
我想問為什麼不是f(y)=(1-p)*p^(y-1) ; y=1,2,...,r
還是我搞錯題目意思 煩請高人指點 感謝!!!
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