2、X
3、>2},P{X>3};P{2>p^normcdf(2,3,2)0.3085>>pl=normcdf(5,3,2)Pl=0.8413»p0=pl-p0.5328P{-4〈X〈10}
4、>>p^normcdf(-4,3,2)P=2.3263e-004>>pl=normcdf(10,3,2)0.9998>>p0=pl—pp0=0.9995P{
5、X
6、>2}»p=normcdf(-2,3,2)p=0.0062>>pl=normcdf(2,3,2)0.3085»pO=l-(pl-p)pO二0.6977P{X>3}»p=normcdf(3,3,2)0.5000>>pO:l-ppO=0.5000(2)求满足条件P{X〉c}=1、{〈(:}的常数(^>>c=norminv(0.5,3,2)32.设X~N
7、(40,52),取容量为n的样本，样本均值记作x，(1)若n=36,求x在38与43之间的概率；»p=norracdf(38,40,5/6)0.0082>>pl^normcdf(43,40,5/6)pi二0.9998>>pO=pl-ppO二0.9916(2)若n=64,求x与总体均值之差不超过1的概率;>>p=normcdf(8/5,0,1)»pl=normcdf(-8/5,0,1)pi二0.0548>>p0=p-plp0=0.89041.某炼钢厂生产一种25MnSi的钢，由于各种偶然因素的影响，各炉钢的含S
8、i量是有些差异的，下面是120炉正常生产的25MnSi钢的含Si量的数据记录(百分数)：0.860.830.770.810.810.800.790.820.820.810.810.870.820.780.800.810.870.810.770.780.770.780.770.770.770.710.950.780.810.790.800.770.760.820.800.820.840.790.900.820.790.820.790.800.760.780.830.750.820.780.730.830.810
9、.810.830.890.810.860.820.820.780.840.840.840.810.810.740.780.780.800.740.780.750.790.850.750.740.710.880.820.760.850.730.780.810.790.770.780.810.870.830.650.640.780.750.820.800.800.770.810.750.830.900.800.850.810.770.780.820.840.850.840.720.850.840.820.850.
10、840.780.78(1)计算均值、标准差、极差、偏度、峰度，画出直方图；»x=[0.860.830.770.810.810.800.790.820.820.810.810.870.820.780.800.810.870.810.770.780.770.780.770.770.770.710.950.780.810.790.800.770.760.820.800.820.840.790.900.820.790.820.790.800.760.780.830.750.820.780.730.830.810.81
11、0.830.890.810.860.820.820.780.840.840.840.810.810.740.780.780.800.740.780.750.790.850.750.740.710.880.820.760.850.730.780.810.790.770.780.810.870.830.650.640.780.750.820.800.800.770.810.720.750.850.830.840.900.820.800.850.810.770.780.820.850.840.780.78];0.8
12、40.850.84均值»e=mean(x)0.8012标准差»b=std(x)b=0.0453极差»r=range(x)0.3100偏度>skewness(x)ans=-0.2931峰度»f=kurtosis(x)f=4.9638hist(x，10)35_30-25-20-15-10-5-0-0.60.650.70.750.80.850.90.951(1)估计并检验其均值。>>[h,p,ci]=tt
