www.fltk.net > 设ξ~B(n,p),如果Eξ=12,Dξ=4,则n和p分别为(...

设ξ~B(n,p),如果Eξ=12,Dξ=4,则n和p分别为(...

∵ξ~B(n,p),Eξ=3,D(2ξ+1)=9,∴Dξ= 9 4 ∴np=3,①np(1-p)= 9 4 ②∴ ② ① 得1-p= 3 4 ∴p= 1 4 ∵ 1 4 n=3 ∴n=12故答案为:12; 1 4 .

∵ξ~B(n,她),Eξ=3,D(七ξ+1)=9,∴Dξ=9一∴n她=3,①n她(1-她)=9一&nbs她; ②∴②①得1-她=3一∴她=1一∵1一n=3∴n=1七故答案为:1七;1一.

∵ξ服从二项分布B~(n,p)由Eξ=2.4=np,Dξ=1.44=np(1-p),可得1-p= 1.44 2.4 =0.6,∴p=0.4,n= 2.4 0.4 =6.故选B

∵随机变量ξ~B(n,p),E(ξ)=1.6,D(ξ)=1.28,∴np=1.6,①np(1-p)=1.28 ②把①代入②得1-p= 1.28 1.6 =0.8,∴p=0.2∵np=1.6∴n=8,故选A.

∵随机变量ξ服从二项分布ξ~B(16,P),且Dξ=3,∴Dξ=16P(1-P)=3,∴P= 1 4 或P= 3 4 ∴Eξ=nP=4或12.故选C.

回答: Eξ=3/4=2p 所以:p=3/8 Dη=np(1-p) =4X 3/8 X 5/8 =15/16

∵ξ服从二项分布B~(n,p)由Eξ=2.4=np,Dξ=1.44=np(1-p),可得p=0.4,n=6.故选:C.

∵ξ服从二项分布B~(n,p)由Eξ=2.4=np,Dξ=1.44=np(1-p),可得1-p=1.442.4=0.6,∴p=0.4,n=2.40.4=6.故选B.

∵随机变量ξ~N(0,1),∴正态曲线关于x=0对称,∵P(ξ>1)=p,∴P(ξ<-1)=p,∴P(-1<ξ<0)= 1 2 -p,故选D.

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