帮解答几道数学题

jin_dida

请把解题方法的连接给我， 谢谢。

[此贴子已经被作者于2008-6-22 11:04:44编辑过]

jin_dida

A certain roller coaster has 3 cars, and a passenger is equally likely to ride in any 1 of the 3 cars each time that passenger rides the roller coaster.  If a certain passenger is to ride the roller coaster 3 times, what is the probability that the passenger will ride in each of the 3 cars?

 

A.     0

B.      1/9

C.     2/9

D.     1/3

E.      1

请帮我解答一下

A set of numbers has the property that for any number t in the set, t + 2 is in the set.  If –1 is in the set, which of the following must also be in the set?

 

I.                   -3

II.                1

III.             5

 

 

A.  I only

B.  II only

C.  I and II only

D.  II and III only

E.  I, II, and III

In a corporation, 50 percent of the male employees and 40 percent of the female employees are at least 35 years old.  If 42 percent of all the employees are at least 35 years old, what fraction of the employees in the corporation are females?

 

A.   3/5

B.    2/3

C.   3/4

D.   4/5

E.    5/6

If 10⁵⁰ – 74 is written as an integer in base 10 notation, what is the sum of the digits in that integer?

 

A.   424

B.    433

C.   440

D.   449

E.    467

A photographer will arrange 6 people of 6 different heights for photograph by placing them in two rows of three so that each person in the first row is standing in front of someone in the second row.  The heights of the people within each row must increase from left to right, and each person in the second row must be taller than the person standing in front of him or her.  How many such arrangements of the 6 people are possible?

 

A.   5

B.    6

C.   9

D.   24

E.    36

For any positive integer n, the sum of the first n positive integers equals [n(n+1)]/2.  What is the sum of all the even integers between 99 and 301?

 

A.   10,100

B.    20,200

C.   22,650

D.   40,200

E.    45,150

jin_dida

怎么都不知道如何得出答案。谢谢。我比较笨

xyzlsh01

1. 1*2/3*1/3=2/9

2. -1+2=1,1+2=3,3+2=5

3. 40%*x+50%*(1-x)=42% =>x=20%

4. 10^50，也就是1的后面有50个0，共51位，减去74后，变为50位。最后两位变成26，前面48位变成48个9。48*9+2+6=。。。.其实，用1000，10000归纳一下也行。

5. I don't know

6. 题目即是求2*（50+52+...+150），它等于2*（150*151/2-50*51/2）

driftysnail

5. 是选A么？

第二排的人都要比第一排的人高， 所以最矮的人肯定是在第一排，并且因为从低到高的排练顺序，最矮的人必须是在最边上的。

就拿 1-6 6个数字来举例的话，第一排的顺序只有， 123， 124， 125， 134，135，5种情况，

shierting

5.是选A.

补充下楼上的: 按照题目要求,可以得出最矮的必然排在第一排最左边,最高的必然排在第二派最右边,所以 再根据楼上编号来排,就有5种排法.

sonntac

第四个，减了以后，肯定是99....926，如果加1就可以被9整除了，答案里面只有440+1可以被9整除,就440了