我又來問功課了[Probability]

Q:X is a random variable defined at X=0,1,2,3,4 such that P(X<r)=[2^(r)-1]/31 for r=1,2,3,4,5. Represent the probability distribution of X by a mathematical formula.

A:2^(r)/31 for r=0,1,2,3,4

又唔識做啦

嘩...... 樹大招風。

冇書响度，唔能夠 refine 個 answer，不過大致係咁：

P(X)=P(X<r)-P(X<r-1)
= (2^r-1)/31 - [2^(r-1)-1]/31
= {2[2^(r-1)]-1 - 2^(r-1)+1}/31
= [(2-1)2^(r-1)-1+1]/31
= [2^(r-1)]/31 ............(r=1,2,3,4,5)
or
= 2^r/31 .....................(r=0,1,2,3,4)

孖吉 發表於 2011-9-29 18:56
冇書响度，唔能夠 refine 個 answer，不過大致係咁：

P(X)=P(X

我明白啦~
真係好多謝你呀~