This topic has been archived. It cannot be replied.
-
工作学习 / 求学深造 / 问题：概率问题，谢谢回答！A fair die is rolled 12000 times. let S be the total number of sixes.Use the Central Limit Theorem to find P(1900<S<2200) in terms of φ , the standard novmal distribution function.
E(S)=12000/6=2000
Var(S) = 12000(1/6)(5/6) = 5000/3
这是正确的解的一部分，请问为什么Var(S)要这样算．
-feiwen(如花笑颜);
2003-2-9
{289}
(#1030721@0)
-
This is a case of normal limit of Binominal DistributionEvery single toss of the dice is a binominal distribution (BD).
For BD, we have:
p(six) = 1/6
and,
var(six) = p(six) * (1-p(six)) = 1/6 * 5/6.
The central limitation therom says that when you toss the dice for N times,
the mean is equal to N*p(six), and the variable equals N*var(six). Thus we
have
Var(S) = N*var(six) = 12000*1/6*5/6.
Q.E.D.
-arron(arron);
2003-2-9
{359}
(#1030776@0)
-
:D,谢谢！！:D
-feiwen(如花笑颜);
2003-2-9
(#1031570@0)