20/06/28 21:16:29.69 DrzpFm0+.net
>>774
(1)
n=1000, p=0.001 とおくと
P(X=k) = C[n,k]･(1-p)^(n-k)･p^k
P(X≦2) = P(X=0) + P(X=1) + P(X=2)
= 0.367695425 + 0.368063488 + 0.184031744
= 0.919790657
(2)
E(X) = Σ[k=1,n] k･P(X=k)
= Σ[k=1,n] k･C[n,k]･(1-p)^(n-k)･p^k
= n･p Σ[k=1,n] C[n-1,k-1] (1-p)^(n-k)･p^(k-1)
= n･p
= 1000・0.001
= 1,