已选分类
理学数学
单选题The average (arithmetic mean) of five number is 26. After one of the numbers is removed, the average (arithmetic mean) of the remaining numbers is 25. What number has been removed? (A) 20 (B) 25 (C) 26 (D) 30 (E) 32
单选题Last year, a certain public transportation system sold an average (arithmetic mean) of 41,000 tickets per day on weekdays (Monday through Friday) and an average of 18,000 tickets per day on Saturday and Sunday. Which of the following is closest to the total number of tickets sold last year? (A) 1 million (B) 1.25 million (C) 10 million (D) 12.5 million (E) 125 million
单选题设有二维随机变量(X，Y)，已知D(X)=9，D(Y)=4，X，Y的相关系数为，则D(X-Y)=______。A.15B.9C.13D.5
单选题Jerome wrote each of the integers 1 through 20, inclusive, on a separate index card. He placed the cards in a box, then drew cards one at a time randomly from the box, without returning the cards he had already drawn to the box. In order to ensure that the sum of all the cards he drew was even, how many cards did Jerome have to draw?
单选题 ADVANCED PURCHASE DISCOUNTS FOR AIRLINE TRAVEL Days Prior to Departure Percentage Discount 0～6 days 0% 7～13 days 10% 14～29 days 25% 30 days or more 40% The table above shows the discount structure for advanced purchase of tickets at a particular airline. A passenger bought a ticket at this airline for$1,050. The ticket agent informed her that, had she purchased the ticket one day later, she would have paid $210 more. How many days before her departure did she purchase her ticket? (A) 6 days (B) 7days (C) 13 days (D) 14 days (E) 29days
单选题Theproductofthetwo-digitnumbersaboveisthethree-digitnumber□◇□,where□,△,and◇,arethreedifferentnonzerodigits.If□×△＜10,whatisthetwo-digitnumber□△?
单选题设ξ1，ξ2是n元非齐次线性方程组Ax=b的两个解，A为n阶方阵，则下列命题成立的是______。
A.Ax=0只有零解
B.|A|≠0
C.存在一个非零向量与A的每一个行向量都正交
D.不存在非零向量与A的每一个行向量都正交
单选题某企业计划在两年内将年产值增加20%，但第一年产值比上一年反而下降5%，那么要达到预期目标，第二年产值要比第一年产值增加幅度为______． A．26.3% B．30.3% C．35.3% D．25%
单选题
单选题微分方程(2x-y)dx+(2y-x)dy=0的通解为______。(C为任意常数)
A.x2+xy+y2=C
B.x2-xy+y2=C
C.2x2-xy+3y2=C
D.2x2+xy+3y2=C
单选题A car dealer who gives a customer a 20 percent discount on the list price of a car still realizes a net profit of 25 percent of cost. If the dealer's cost is $4800, what is the usual list price of the car? (A) $6000 (B) $6180 (C) $7200 (D) $7500 (E) $8001
单选题设A、B、C均为n阶可逆矩阵，且ABC=E，则下列结论成立的是______。
A.ACB=F
B.BAC=E
C.BCA=E
D.CBA=E
单选题Paul is standing 180 yards due north of point P, Franny is standing 240 yards due west of point P. What is the shortest distance between Franny and Paul?
单选题OnMonday,acertainanimalshelterhoused55eatsanddogs.ByFriday,exactlyoftheeatsandofthedogshadbeenadopted;nonewcatsordogswerebroughttotheshelterduringthisperiod.WhatisthegreatestpossiblenumberofpetsthatcouldhavebeenadoptedfromtheanimalshelterbetweenMondayandFriday?(A)11(B)12(C)13(D)14(E)20
单选题两个班A和B在某次考试中的分数如下表所示：问当A和B两个班的学生合在一起时，其学生考试分数的算术平均值是否大于其中数? median average score A 80 82 B 78 74 (1)A班有37人，B班有40人。 (2)A和B两个班共有77人
单选题一艘小轮船上午8:00起航逆流而上(设船速和水流速度一定)，中途船上一块木板落入水中，直到8:50船员才发现这块重要的木板丢失，立即调转船头去追，最终于9:20追上木板．由上述数据可以算出木板落水的时间是( )． A．8:35 B．8:30 C．8:25 D．8:20 E．8:15
单选题假设甲、乙两国关于拥有洲际导弹数量的关系曲线y=f(x)和x=g(y)的意义是：当甲国拥有导弹x枚时，乙国至少需储备导弹y=f(x)枚，才有安全感：当乙国拥有导弹y枚时．甲国至少需储备导弹x=g(y)枚，才有安全感．这两条曲线将坐标平面的第一象限分成四个区域Ⅰ，Ⅱ．Ⅲ，Ⅳ，如图图5—1所示．双方均有安全感的区域是()．A．Ⅰ和ⅢB．ⅢC．ⅡD．Ⅱ和ⅣE．Ⅳ
单选题 ADVANCED PURCHASE DISCOUNTS FOR AIRLINE TRAVEL Days Prior to Departure Percentage Discount 0～6 days 0% 7～13 days 10% 14～29 days 25% 30 days or more 40% The table above shows the discount structure for advanced purchase of tickets at a particular airline. A passenger bought a ticket at this airline for$1,050. The ticket agent informed her that, had she purchased the ticket one day later, she would have paid $210 more. How many days before her departure did she purchase her ticket?
单选题During a sale at an office supply store, for every box of paper clips purchased for 15 cents, a second box can be purchased for 4 cents. How many boxes of paper clips did Paul buy if he spent 91 cents on boxes of paper clips? (A) 6 (B) 7 (C) 8 (D) 9 (E) 10
单选题若f(x)为连续函数且满足关系式，则f(9)=______。A．B．1C．0D．-1