B(n,p)中X,B,N,
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B(n,p)中X,B,N,
![B(n,p)中X,B,N,](/uploads/image/z/8635370-50-0.jpg?t=B%28n%2Cp%29%E4%B8%ADX%2CB%2CN%2C)
B(n,p),N,P是随机变量,
如设X~B(n,p),n=4.如果P{X=1}=P{X=2},则p=( )
由X~B(n,p),n=4可知
P{X=1}=C(4,1)×p×(1-p)^3=4p×(1-p)^3
P{X=2}=C(4,2)×p^2×(1-p)^2=6p^2×(1-p)^2
由P{X=1}=P{X=2},
故4p×(1-p)^3=6p^2×(1-p)^2,
即4(1-p)=6p
解得p=0.4
如设X~B(n,p),n=4.如果P{X=1}=P{X=2},则p=( )
由X~B(n,p),n=4可知
P{X=1}=C(4,1)×p×(1-p)^3=4p×(1-p)^3
P{X=2}=C(4,2)×p^2×(1-p)^2=6p^2×(1-p)^2
由P{X=1}=P{X=2},
故4p×(1-p)^3=6p^2×(1-p)^2,
即4(1-p)=6p
解得p=0.4