习题三1.正常情况下,某炼铁炉的铁水含碳量24.55,0.108XN.现在测试了5炉铁水,其含碳量分别为4.28,4.40,4.42,4.35,4.37.如果方差没有改变,问总体的均值有无显著变化?如果均值没有改变,问总体方差是否有显著变化0.05?解由题意知,24.55,0.108XN,5n,5114.3645iixx,0.05,5220110.095265iisx.1)当00.108已知时,①设统计假设0010:4.55,:4.55HH.②当0.05时,0.975121.96uu,临界值120.1081.960.09475cun,拒绝域为000{}{0.0947}Kxcx.③004.3644.550.186xK,所以拒绝0H,接受1H,即认为当方差没有改变时,总体的均值有显著变化.2)当04.55已知时,①设统计假设2222220010:0.108,:0.108HH.②当0.05时,临界值222210.02520.975122111150.1662,52.566655cncnnn,拒绝域为222202122220000{}{2.56660.1662}ssssKcc或或.③202200.095268.16700.108sK,所以拒绝0H,接受1H,即均值没有改变时,总体方差有显著变化.2.一种电子元件,要求其寿命不得低于1000h.现抽取25件,得其均值950xh.已知该种元件寿命2,100XN,问这批元件是否合格0.05?解由题意知,2,100XN,25n,950x,0.05,0100.①设统计假设0010:1000,:1000HH.②当0.05时,0.051.65uu,临界值1001.653325cun,拒绝域为000{}{33}Kxcx.③00950100050xK,所以拒绝0H,接受1H,即认为这批元件不合格.3.某食品厂用自动装罐机装罐头食品,每罐标准质量为500g,现从某天生产的罐头中随机抽测9罐,其质量分别为510,505,498,503,492,502,497,506,495(单位:g),假定罐头质量服从正态分布.问1)机器工作是否正常0.05?2)能否认为这批罐头质量的方差为25.50.05?解设X表示用自动装罐机装罐头食品每罐的质量(单位:g).由题意知2500,XN,方差2未知.9n,911500.88899iixx,0.05,222111133.6111118nniiiisxxxxn,52201130.66679iisx1)①设统计假设0010:500,:500HH.②0.97512182.306tnt,临界值125.797512.3064.45649sctnn,拒绝域为000{}{4.4564}Kxcx.③00500.88895000.8889xK,所以接受0H,拒绝1H,即认为机器工作正常.2)当0500已知时,①设统计假设2222220010:5.5,:5.5HH.②当0.05时,临界值222210.02520.975122111190.3,92.113399cncnnn,拒绝域为222202122220000{}{2.11330.3}ssssKcc或或.③2022030.66671.013785.5sK,所以接受0H,拒绝1H,即为这批罐头质量的方差为25.5.4.某部门对当前市场的鸡蛋价格情况进行调查,抽查某市20个集市上鸡蛋的平均售价为3.399元/500克,标准差为0.269元/500克.已知往年的平均售价一直稳定3.25元/500克左右,问该市场当前的鸡蛋售价是否明显高于往年0.05?解由题意知,23.25,XN,20n,3.399x,0.05,0.269s.①设统计假设0010:3.25,:3.25HH.②当0.05时,10.951191.729tnt,临界值10.26911.7290.106719sctnn,拒绝域为000{}{0.1067}Kxcx③003.3993.250.149xK,所以拒绝0H,接受1H,即认为市场当前的鸡蛋售价是明显高于往年.5.已知某厂生产的维尼纶纤度2,0.048XN,某日抽测8根纤维,其纤度分别为1.32,1.41,1.55,1.36,1.40,,1.50,1.44,1.39,问这天生产的维尼纶纤度的方差2是否明显变大了0.05?解由题意知2,0.048XN,8n,8111.421258iixx,0.05,22211110.0122118nniiiisxxxxn.①设统计假设2222220010:0.048,:0.048HH.②当0.05时,临界值2210.9511172.0117cnn,拒绝域为2202200{}{2.01}ssKc.③202200.012215.29950.048sK,所以拒绝0H,接受1H,即这天生产的维尼纶纤度的方差2明显变大了.6.某种电子元件,要求平均寿命不得低于2000h,标准差不得超过130h.现从一批该种元件中抽取25个,测得寿命均值为1950h,标准差148sh.设元件寿命服从正态分布。试在显著性水平0.05下,确定这批元件是否合格.解设X表示这批元件的寿命,由题意知22000,130XN,25n,1950x,0.05,148s.1)①设统计假设0010:2000,:2000HH.②当0.05时,0.051241.711tnt,临界值14811.71150.645625sctnn,拒绝域为000{}{50.6456}Kxcx.③001950200050xK,所以接受0H,拒绝1H,即认为这批元件平均寿命不得低于2000h.2)①设统计假设2222220010:130,:130HH.②当0.05时,临界值2210.95111241.5175124cnn,拒绝域为2202200{}{1.5175}ssKc.③2202201481.2961130sK,所以接受0H,拒绝1H,即认为这批元件标准差不超过130h.所以这批元件合格.7.设12,,,nXXX为来自总体,4XN的样本,已知对统计假设0:1;H1:2.5H的拒绝域为02KX.1)当9n时,求犯两类错误的概率与;2)证明:当n时,0,0.解1),4XN,01:1,:2.5,HH02KX,9n.12121991.522XPXP11.50.0668,2.522.522.5990.7522XPXP0.7510.750.2266.2),4XN,01:1,:2.5,HH02KX.1212110,2222XnnPXPnnn,2.522.522.510,2244XnnPXPnnn8.设需要对某一正态总体,4XN的均值进行假设检验01:15;:15HH取检验水平0.05,试写出检验0H的统计量和拒绝域.若要求当1H中的13时犯第Ⅱ类错误的概率不超过0.05,估计所需的样本容量n.解01~(,4),:15;:15XNHH.拒绝域为015KXc,统计量为23.301.65cunnn.3.3023.30151313nPXPXnn13131.6511.650.0522XXPnnPnn,20.95(1.65)0.95,1.651.65,3.30,3.311nnunn.所需的样本容量11n.9.设12,,,nXXX来自总体20,XN的样本,20为已知,对假设00:H,11:H,其中01,试证明22011210nuu.解由题意知20,XN,且20为已知,故01cun,拒绝域为0001Kxun.01 XP(+c=)1011100()?XPnun1010()un,所以1011uun,22101120nuu,即22011210nuu.10.设1217,,,XXX为来自总体20,XN样本,对假设2201:9,:3.319HH的拒绝域204Ks.求犯第Ⅰ类错误的概率和犯第Ⅱ错误的.解由题意知20,XN,2202499sPWK,24117917c,查表得0.025;220243.3193.314sPWK,2141173.31417c,查表得0.25.11.设总体的密度函数为1,01,;0,.xxfx其他,统计假设0:=1H,1:=2H.现从总体中抽取样本12,XX,拒绝域02134KXX,求:犯两类错误的概率,.解当0:=1H成立时,1,01,;0,.xfx其他0213114PWKPXX1314321040.2510.250.75ln0.75xdxdx;当1:=2H成立时,2,01,;0,.xxfx其他0213224PWKPXX1314312210433994ln0.7544168xxxdxdx.12.设总体2,XN,根据假设检验的基本原理,对统计假设:20011101):,:HH已知;200102):,:HH未知,试分析其拒绝域.解1)因为2,XN,所以2,XNn,即0,1XNn,当2已知时,10XPuHn,即10uPXn,所以拒绝域为100uKXn.2)因为2,XN,所以2,XNn,即0,1XNn,当2未知时,用2S作为2的近似,则1XtnSn,01XPtnHSn,即01StnPXn,所以拒绝域为001stnKXn.13.设总体2,XN根据假设检验的基本原理,对统计假设:222200101):,:HH