GWD数学，哪位牛人讲解一下

happylxm · 发表于 2011-5-10 10:54:39

1.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
答案是C， how come?
2.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
答案C，totally have no idea~~
3.A total of $60,000 was invested for one year.But of this amount earned simple annual interest at the rate of x percent per year, and the rest earned simple annual interest at the rate of y percent per year.If the total interest earned by the $60,000 for that year was $4,080, what is the value of x?

(1)x = (3/4) y

(2)The ratio of the amount that earned interest at the rate of x percent per year to the amount that earned interest at the rate of y percent per year was 3 to 2
题目中的 the rest 是指的什么啊？答案C

4.Joanna bought only $0.15 stamps and $0.29 stamps.How many $0.15 stamps did she buy?

(1)She bought $4.40 worth of stamps.

(2)She bought an equal number of $0.15 stamps and $0.29 stamps.

答案D，费解啊……

5.On a certain transatlantic crossing, 20 percent of a ship’s passengers held round-trip tickets and also took their cars abroad the ship.If 60 percent of the passengers with round-trip tickets did not take their cars abroad the ship, what percent of the ship’s passengers held round-trip tickets?
A.33 1/3
B.40%
C.50%
D.60%
E.66 2/3% 答案C

6.A collection of 36 cards consists of 4 sets of 9 cards each.The 9 cards in each set are numbered 1 through 9.If one card has been removed from the collection, what is the number on that card?

(1)The units digit of the sum of the numbers on the remaining 35 cards is 6.

(2)The sum of the numbers on the remaining 35 cards is 176.

答案D,虽然选对了，但是不知道第二个怎么也是对的

7.What is the median number of employees assigned per project for the projects at Company Z?

(1)25 percent of the projects at Company Z have 4 or more employees assigned to each project.

(2) 35 percent of the projects at Company Z have 2 or fewer employees assigned to each project.
答案C，中数应该是在35%里吧？但是中数到底是2还是1呢

在此先谢谢各位了！

LAL · 发表于 2011-5-10 11:14:03

1. (C1 3*C1 2*C1 1)/3^3=2/9
2.10^50-74=999...9926(一共48个9）这样每一位数的数字之和就是48*9+2+6=440
3.（1）（2）两个条件加在一起才能列出二元一次方程组解出答案，36000x+24000y=4080（第二个条件提供的式子），这样在加上（1）就能解出x和y了
4.我觉得选A，条件（1）下，只有10个0.15和10个0.29这一种组合能凑出4.40
5.设买来回票的人的百分比是x，0.2/x%+0.6=1或者20+60*x%=x%
6.对于（1），最初36张牌点数之和是4*(1+...+9)=4*45=180 当拿掉一张之后，可能的点数和为171-179，如果尾数告诉你是6 那就只能是176，即拿掉的是4
对于（2）同理
7.如果按照人数从小到大排的话，前35%是小于等于2，后25%大于等于4，所以中间的40%是3，而中位数求的就是最中间那个数，在这里就应该是第50%那个数，显然是3

kikisunflower · 发表于 2011-5-10 11:24:09

7题median number是3

前35%，=<2

后25%，>=4

中间有40%，=3

中位数在中间的这40%里面

kikisunflower · 发表于 2011-5-10 11:25:27

6题，条件2，
sum=180，减掉176，=4，拿走的数是4

条件2 is sufficient

kikisunflower · 发表于 2011-5-10 11:33:42

5题，
   Round-trip 非round-trip
Car abroad   A
Car not abroad   B

设总人数X

条件1：20 percent of a ship’s passengers held round-trip tickets and also took their cars abroad the ship: A=20%X
条件2：60 percent of the passengers with round-trip tickets did not take their cars abroad the ship: B=60%*(A+B)→2B=3A→B=30%X

Round-trip的人=A+B=50%X，选C

happylxm · 发表于 2011-5-15 01:10:16

2.10^50-74=999...9926(一共48个9）这样每一位数的数字之和就是48*9+2+6=440

-- by 会员 LAL (2011/5/10 11:14:03)

[/quote]

题中的这句an integer in base 10 notation是什么意思呢？应该写成什么养的表达式啊

GWD数学，哪位牛人讲解一下

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