已选分类
理学数学
单选题x，y，z为正整数，且x＜y＜z，求y? (1)x+y+z=6 (2)xyz=6 (A) 条件(1)充分，但条件(2)不充分． (B) 条件(2)充分，但条件(1)不充分． (C) 条件(1)和(2)单独都不充分，但条件(1)和条件(2)联合起来充分． (D) 条件(1)充分，条件(2)也充分． (E) 条件(1)和条件(2)单独都不充分，条件(1)和条件(2)联合起来也不充分．
单选题The trip was 40 miles. The speed for the first y miles was x, and the speed for the remaining trip was 1.2x. What is the average speed? (1)x=12 miles per hour (2)y=20 miles
单选题If r and s are integers and rs+r is odd, which of the following must be even? (A) r (B) s (C) r+s (D) rs-r (E) r2+s
单选题If cylinder P has a height twice that of cylinder Q and a radius half that of cylinder Q, what is the ratio between the volume of cylinder P and the volume of cylinder Q?
单选题约等于几?
单选题随机变量ξ=X+Y与η=X-Y不相关的充要条件为______。
A.E(X)=E(Y)
B.D(X)=D(Y)
C.D(X2)=D(Y2)
D.E(X2)+(E(X))2=E(Y2)+(E(Y))2
单选题WhatistheperimeterofpentagonVWXYZshownabove?
单选题已知关于x的一元二次方程k2x2-(2k+1)x+1=0有两个相异实根，则k的取值范围是______．
单选题The width of a rectangle is 6 cm less than the length. If the perimeter of the rectangle is 48 cm, what is the length of the rectangle in centimeters?
单选题The trip was 40 miles. The speed for the first y miles was x, and the speed for the remaining trip was 1.2x. What is the average speed? (1)x=12 miles per hour (2)y=20 miles (A) 条件(1)充分，但条件(2)不充分． (B) 条件(2)充分，但条件(1)不充分． (C) 条件(1)和(2)单独都不充分，但条件(1)和条件(2)联合起来充分． (D) 条件(1)充分，条件(2)也充分． (E) 条件(1)和条件(2)单独都不充分，条件(1)和条件(2)联合起来也不充分．
单选题The arithmetic mean of a data set is 46 and the standard deviation of the set is 4. Which value is exactly 1.5 standard deviations from the arithmetic mean of the set?
单选题
单选题If the value of a piece of property decreases by 10 percent while the tax rate on the property increases by 10 percent, what is the effect on the taxes? (A) Taxes increase by 10 percent. (B) Taxes increase by 1 percent. (C) There is no change in taxes. (D) Taxes decrease by 1 percent. (E) Taxes decrease by 10 percent.
单选题设函数f(x，y)连续，交换二次积分次序=______。A．B．C．D．
单选题A computer is programmed to generate a list of multiples of prime numbers 2, 3, and 5, as shown below： Program 1-List multiples of 2 Program 2-List multiples of 3 Program 3-list multiples of 5 How many integers between 1 and 100 will appear on all three of the lists of the programs produced above? (A) None (B) 1 (C) 3 (D) 5 (E) An infinite number of integers
单选题设随机变量X，Y均服从正态分布，X～N(μ，42)，Y～N(μ，52)，记p1=P{X≤μ-4}，p2=P{Y≥μ+5}，则______。
A.对任何实数μ，都有p1=p2
B.对任何实数μ，都有p1＜p2
C.只有对μ的个别值，才有p1=p2
D.对任何实数μ，都有p1＞p2
单选题$ 2000 is deposited into a savings account that earns interest at the rate of 10 percent per year, compounded semiannually. How much money will there be in the account at the end of one year?
单选题A person is standing on a staircase. He walks clown 4 steps, up 3 steps, down 6 steps, up 2 steps, up 9 steps, and down 2 steps. Where is he standing in relation to the step on which he started?
单选题设随机变量X服从(-1，1)上的均匀分布，事件A={0＜X＜1}，B={X||＜}，则______。A.P(AB)=0B.P(AB)=P(A)C.P(A)+P(B)=1D.P(AB)=P(A)·P(B)
单选题Ifthevariables,X,Y,andZtakeononlythevalues10,20,30,40,50,60,or70withfrequenciesindicatedbytheshadedregionsabove,forwhichofthefrequencydistributionsisthemeanequaltothemedian?