求教各位~~帮帮菜鸟的我一个忙吧~~绿皮数学OG...

pumengqi · 发表于 2010-7-25 23:43:04

P75,110题
A certain clock marks every hour by striking a number of times equal to the hour, and the time required for a stroke is exactly equal to the time interval between strokes . At 6:00 the time lapse between the begining og the first stroke and the end of the last stroke is 22 seconds. At 12:00, how many seconds elapse between the begining of the first stroke and the end of the last stroke?
(A) 72, (B) 50, (C) 48, (D) 46, (E) 44.
P79, 132题
A company that ships boxes to a total of 12 distribution centers uses color coding to identify each center. If either a single color or a pair of two different colors is chosen to represent each center and if each center is uniquely represented by that choice of one or two colors, what is the minium number of colors needed for the coding?(Assume that the order of the colors in a pair does not matter.)
(A) 4, (B) 5, (C) 6, (D) 12, (E) 24.
以上两道题，我实在没有读懂题意，看了后面的解释也懵懵懂懂的，希望大家给我讲解一下.
P78, 131题
In the sequence X0,X1, X2.....,Xn, each term from X1 to Xk is 3 greater than the previous term, and each term from Xk+1 to Xn is less than the previous term, where n and k are positive integers and k<n. If X0=Xn=0 and if Xn=15, what is the value of n?
(A) 5, (B) 6, (C) 9, (D) 10, (E) 15.
老师，这道题目考的是等差数列的知识点，但是由题可知， X1到Xk是一个等差为3的递增数列，而Xk+1 到Xn 是一个等差为-3的递减数列。
根据绿皮OG 后面的分析，如下：
Since X0=0 and each term from X1 to Xk is 3 greater than the precious term, then Xk=0+(k)(3). Since Xk=15, then 15=3k and k=5.
Since each term, then Xn=Xk-(n-k)(3). Subsituting the known values for Xk, Xn, and k gives
0=15-(n-5)(3), from which it follows that 3n=30 and n=10.
我的问题是，从题目，我无法判断出Xk与Xk+1是什么关系，属于哪种数列，而上面OG解析红色部分，却用Xk代入方程解题，我对于这个方法，不同意。但是，如果用Xk+1代入解题则无法得出N的值，烦请告诉我，到底我哪里想的不对.
谢谢大家的帮助！

拜谢....继续拜....

lengyueshuang · 发表于 2010-7-26 09:26:34

P75,110题

选D 46
打击一下所需时间=22/(5+6)=2 5为间隔，6为打击次数
所以12点时需要时间=2*（11+12）=46

lengyueshuang · 发表于 2010-7-26 09:31:18

A company that ships boxes to a total of 12 distribution centers uses color coding to identify each center. If either a single color or a pair of two different colors is chosen to represent each center and if each center is uniquely represented by that choice of one or two colors, what is the minium number of colors needed for the coding?(Assume that the order of the colors in a pair does not matter.)

这题是选5吗
5种颜色总的有15种组合>12,我个人觉得

fullmoon558 · 发表于 2010-7-26 10:43:35

第一题我得出的是D，46s，第二题和LS的一样，5个。
第一题我来翻译下吧，就是说，一个钟在整点的时候会敲，到几点敲几下，而在敲两下中间的一个时间间隔等于敲一下的时间，它又说，在六点的时候，从敲第一下到最后一下（也就是第六下)持续了22秒，问你在12点的时候，从第一下到最后一下能持续多少时间。
第二题呢，就是说有个公司要把货物运到12个不同的分配中心去，然后要用一个单独的颜色或者是一对颜色（由两个不同的颜色组成）来代表着12个不同的分配中心，问最少需要几个颜色

fullmoon558 · 发表于 2010-7-26 10:49:54

对于第三题，LZ的疑问可以从这里解答：each term from Xk+1 to Xn is less than the PREVIOUS term。那么就是说，Xk+1比Xk要小。但这里我有个疑问，题中并没有给小多少，又是怎么知道是小三的呢

pumengqi · 发表于 2010-7-26 12:58:30

那个2解出来应该是表示每次敲钟的间隔时间为2S，我不明白为什么敲6次要+5次的间隔。也就是题目中，the time required for a stoke is exactly equal to the time interval bewteen strokes.

pumengqi · 发表于 2010-7-26 13:00:47

谢谢大侠的仗义帮助~~

pumengqi · 发表于 2010-7-26 13:01:22

谢谢您的帮助~~~~！！！

fullmoon558 · 发表于 2010-7-26 13:27:56

LZ我的疑问你没有解答啊，第三题中从Xk+1到X n中那个等差3是哪里来的？
“each term from Xk+1 to Xn is less than the previous term”原题中并没有给出3啊？
LZ是不是题抄错了？

贝西文迅 · 发表于 2017-10-1 20:40:04

Mark一下！

求教各位帮帮菜鸟的我一个忙吧绿皮数学OG...

对于那个间隔5，我还是存在疑问

懂了..茅塞顿开了...

解释的真清楚~

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