几道PREP题~~跪求大N帮助啊~~泪奔了~~

Michiko54

1、Alice's take-home pay last year was the same each month, and she saved the same fraction of her take-home pay each month.  The total amount of money that she had saved at the end of the year was 3 times the amount of that portion of her monthly take-home pay that she did not save.  If all the money that she saved last year was from her take-home pay, what fraction of her take-home pay did she save each month?

(A) 1/2
(B) 1/3
(C) 1/4
(D) 1/5
(E) 1/6
这题怎么做？答案是D

2、If M=4^1/2+4^1/3+4^1/4,then the value of M is
(A) less than 3
(B) equal to 3
(C) between 3 and 4
(D) equal to 4
(E) greater than 4
答案是E，怎么做啊？找不到思路~~

3、When a certain tree was first planted, it was 4 feet tall, and the height of the tree increased by a constant amount each year for the next 6 years.  At the end of the 6th year, the tree was 1/5 taller than it was at the end of the 4th year.  By how many feet did the height of the tree increase each year?

(A)  3/10
(B)  2/5
(C)  1/2
(D)  2/3
(E)  6/5
答案是D，可是我算出来是1/10，我列的式子是 4+5n-(4+3n)=1/5

gengyi130

第一题就是 设个portion为X  12(1*X)=3(1-X)

gengyi130

第二题 你想一下， 4开根号等于2，4^1/3 and 4^1/4虽然算不出来，但是肯定大于1 因为 所以2+两个大于1的数，肯定大于4

gengyi130

第三题就是 列个式子 4+6X= (4+4X)(1.2)

xhm100

2.M=2+4^1/3+2^1/2>2+1+1.414>4
3.4+6n/4n+4n=6/5    => n=2/3  
1/5 means 20 % not feet

niuniupig

第三道题不要多想：每年长X，刚刚种下去的那年不叫第一年，种下去那年过完了，第一年才结束，所以第一年的高度就是4+X，第六年就是4+6X，ok？
然后你1/5理解的不对，如果按你的解法后面应该带上单位，如：第六年长的比第四年高1/5 feet，事实是1/5在这里是个比率，即是第六年比第四年高的值2x=第四年高度的五分之一（1/5（4+4x））。。。。
所以4+6x-（4+4x）=1/5（4+4x）

Michiko54

明白了~~多谢各位大N~~~
还有几道题哇~~~各路大神尽显神通啊~~~
1、For a certain race, 3 teams were allowed to enter 3 members each.  A team earned 6 - n points whenever one of its members finished in nth place, where 1 <= n <= 5.  There were no ties, disqualifications, or withdrawals.  If no team earned more than 6 points, what is the least possible score a team could have earned?

(A) 0
(B) 1
(C) 2
(D) 3
(E) 4
怎么考虑啊~~不会做
2、In a class of 30 students, 2 students did not borrow any books from the library, 12 students each borrowed 1 book, 10 students each borrowed 2 books, and the rest of the students each borrowed at least 3 books.  If the average (arithmetic mean) number of books borrowed per student was 2, what is the maximum number of books that any single student could have borrowed?

(A) 3
(B) 5
(C) 8
(D) 13
(E) 15
【思路】
答案是D    剩10可買 有可能是同一個人買 10+3=13  为什么是这个式子呢？与at least有关吗？
3、John and Mary own shares of stock in a certain company.  Does John own more shares of the company's stock than Mary?

(1) Mary owns more than 500 shares of the company's stock.

(2) The number of shares of the company's stock that John owns is 400 less than twice the number of shares of the company's stock that Mary owns.
【答案】C
【思路】問J>M
(1)M>500     ----------------------------------------------------------------------insufficient
(2) J=2M-400  --------------------------------------------------------------------- insufficient
(1)(2)用數字代入 J>M--------------------------------------------------------------- sufficient
疑问：（1）（2）结合得J>600,M>500,    由这个可以推出J>M吗？若J=650，M=700就不满足了啊

NDIWDNEDW

gengyi130 发表于 2011-10-22 13:06
第二题 你想一下， 4开根号等于2，4^1/3 and 4^1/4虽然算不出来，但是肯定大于1 因为 所以2+两个大于1的数 ...

Mark一下！               

IMCK

xhm100 发表于 2011-10-22 13:13
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同意！               

lanfield

mark一下！