[求助]2个Gmat Prep题－又添了2道

咋顶置区没有找到相关的讨论。

In a certain desk of cards,each card has a positive interger written on it. A child draws a card and multiples the interger on the card by the next large interger. If each possible product is between 15and 200, then the least and greatest intergers could be ?

Key: 4 and 13

完全摸不找思路

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

Key 2/3, 算了N遍也没算出来，555555555555

 新不懂的题

The sum of the first 50 positive even intergers is 2,550. What is sum of even interger from 102 to 200, inclusive?

Key 7550

Store S sold a total of 90 copies of certain book duriing 7 days last week, and it sold different number of copies on any two of days. If for the seven days store S sold the greatest number of copies on Saturday and the second greatest number of cpies on Friday, did store S sell more than 11 copies on Friday?

1. Last week, S sold 8 copies on Thursday.

2. Lsat week, S sold 38 copies on Saturday.

答案选B，我选的E

55555555今天模考又被数学害了。。。

第一道~乘积要在15~200之间~

我的方法是用试的~

假如最小是1,那么1*2=3<15,假如最小是2,那么2*3=6<15...直到最小是4的时候,4*5=20>15

再试最大的~我们都知道13^2=169,=>最大的数字大于13.那么我们来试14,13*14=182<200,再试15,14*15=210>200.因此卡片上的数字最大为13。。。

方法比较笨，但是还是可以得出答案的~~

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

假设树的生长率为Ｒ　ＦＥＥＴ／ＹＥＡＲ

树在第４年的高度为　４（１＋Ｒ）＾４

树在第６年的高度为　４（１＋Ｒ）＾６

又，４（１＋Ｒ）＾６／４（１＋Ｒ）＾４＝５／４

＝＞Ｒ＝．．．

因为做Prep也碰到这个了，所以正打算问就看到哈佛问了，真是great minds think alike啊，哈哈。。。

不好意思蠢蠢地问一句：

题目说的是每年增长相同的FEET，不是每年都以一个Constant Rate增长，那不是等差数列吗？为啥要设生长率为R，不是应该设一个公差为R才对吗？而且如果生长率为R，那不应该是R percentage/YEAR吗？为啥是Ｒ　ＦＥＥＴ／ＹＥＡＲ？

上面的式子约分解的R好像也得不到那个答案哦？

[(4+6r)-(4+4r)]/(4+4r)=1/5

r=2/3

以下是引用betterman2004在2006-8-21 11:29:00的发言：

因为做Prep也碰到这个了，所以正打算问就看到哈佛问了，真是great minds think alike啊，哈哈。。。

不好意思蠢蠢地问一句：

题目说的是每年增长相同的FEET，不是每年都以一个Constant Rate增长，那不是等差数列吗？为啥要设生长率为R，不是应该设一个公差为R才对吗？而且如果生长率为R，那不应该是R percentage/YEAR吗？为啥是Ｒ　ＦＥＥＴ／ＹＥＡＲ？

上面的式子约分解的R好像也得不到那个答案哦？

汗....我错了....我的想法是R percentage/YEAR

而题目应该是 R FEET/YEAR 才对....

嗯,应该是楼上的算法........哈妹...不好意思误导你了.....

以下是引用哈佛情人在2006-8-21 6:48:00的发言：

咋顶置区没有找到相关的讨论。

In a certain desk of cards,each card has a positive interger written on it. A child draws a card and multiples the interger on the card by the next large interger. If each possible product is between 15and 200, then the least and greatest intergers could be ?

Key: 4 and 13

完全摸不找思路

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

Key 2/3, 算了N遍也没算出来，555555555555

 

第一题 由题意可知 15 =< X*(X+1) =<200

由X*(X+1)>=15，可解出 X> (根号61 - 1)/2, 因此最小值为4

由X*(X+1)<=200，可解出  X<(根号801 -1 )/2, 因此最大值为13

谢谢，我也把题理解错了，感觉数学题有时理解起来比RC还难啊。

要是理解出错，我就亏大了！