未知题型 设自动包装机包装的每袋盐的净重服从正态分布,按规定每袋的标准重量为1 kg,标准差不能超过0.02 kg.某天开工后,从装好的食盐中随机地抽取9袋,测其净重为(单位:kg): 0.994 1.014 1.02 0.95 1.03 0.968 0.976 1.048 0.982 问这天包装机工作是否正常?(α=0.05)
单项选择题 根据短文回答 46~50 题。 The Roadrunner The roadrunner(走雀)lives in the desert zone of the southwestern United States and northern Mexico.___________ (46)People gave it its name because they Usually see it running across a road,but of course,it spends more time among the plants of the desert than it does on roads.The roadrunner is quite a large bird-about 45 centimeters long and 25 centimeters high.___________(47)It holds its head straight out in front and its tail sticks straight。Out in back.It takes long steps and can run 30 kilometers an hour.It eats an amazing variety of food.Although it eats plants once in a while,it is mostly a meat eater.Most of its diet is insects,but it also catches birds,mice。and other smile animals.It is even brave enough to catch snakes and black widow spiders(蜘蛛) ___________ (48)When he finds one,he gives her presents-a snake to eat or a tiny branch of a tree to use in building a nest.Then they build their nest,the female lays eggs,and they raise their young.___________ (49) one couple in Arizona feeds a pair of roadrunner that come once at a time every day and make a noise outside the window.If Someone doesn't give the bird a piece of hamburger immediately, the bird knocks on the window with its beak (喙).Roadrunners are not shy.___________ (50)They will stand on a chair or table and watch television and they seem really interested in what is happening on the program.( ) A.Roadrunners can also become friendly with people.B.People laugh when it runs because it looks so funny.C.It is a bird,but it can only fly about as much as a chicken can.D.In early spring.the bird doesn't eat anything.E.Another couple feeds a pair of roadrunners that go right into the house.F.In the spring,a male roadrunner begins looking for a female as a mate. 第 46 题 请选择(46)处的最佳答案
未知题型 某冶金工作者对锰的溶化点作了4次试验,结果分别为(单位:℃)1 269、1 271、1 263、1 265,假定数据服从正态分布,在α=0.05条件下,试检验: ①该工作者对锰溶化点的测量的平均结果是否符合于公布的数字1 260℃; ②侧量结果的标准差是否大于2℃.