lisaislisa

哦 知道你是什么意思了
可是要得到50 必须有5或10
所以是重复计算了

^^

M022girl

以下是引用Mush在2003-1-9 20:41:42的发言：
为什么这样不可以呢？？
[思路]问n最大，就是说24！里可以乘出多少个10
2*50
5*20
10

所以我觉得n=5 
-------------n=5是不应该的。因为20和50里面包括了5和10，这是重复计算啊。

我知道问题在哪里了
[思路]问n最大，就是说24！里可以乘出多少个10
1*2*3*4*5*6*7*8*9*10*11*12*13*14*15*16*17*18*19*20*21*22*23*24
2*5
10
20*5（来自50）

所以n=4

[em09]

lisaislisa

3. There are 20 cars in a dealershop, the cars are of 5 different colors including white cars and red cars. The probablility of picking either a white or red car is less than 3/5. What is the greatest possible number of red cars? [思路]求红车数目的最大可能 已经知道The probablility of picking either a white or red car is less than 3/5 小于3/5的最大的数是4/5 -——》R/20=4/5 红车数目的最大可能是16 ------------------------ how come 4/5is greater than 3/5 i think , if there is at most 3/5 cars are either white or red then the number of white plus red is less than 12 the biggest possible is 11 then at least there should be on white car so the possible largest number of red car is 10 5. What is the value of integer r? a) 4<(r-1)(r-1)<16 b) 4<(r+1)(r-1)<16 ---------------------------- a)=>2 -1 integer r =-2 or 4 b)=>4<5 -root17 r=-4 ,-3 or 3 ,4 combine a)and b)=> r=4 my an is C others agree ^^

Mush

4. Line goes through (5,a). Is the slope<0? 1) Line goes through (a,5) 2) Line goes throug (20,a) [思路]代入a=+-1 (5,1)(1,5) (5,-1)(-1,5) ——slope<0 (5,a). (20,a) slope=0 [确认]D 我觉得你没有考虑a=5的可能。如果a=5，那(1)也就无法判定slope. 所以应该选b.

lisaislisa

Mush : it makes sense !
thx for your warning

^^

mingja

请问内容在那儿

怎么只有标题没有内容?

本周数学JJ总结2003.1.06-2003.1.12[附解题思路]
JJ题目一个都没有?

VICTOR_JZG

以下是引用mingja在2003-1-11 2:41:41的发言：
请问内容在那儿

怎么只有标题没有内容?

本周数学JJ总结2003.1.06-2003.1.12[附解题思路]&nbsp;
JJ题目一个都没有?

原则上本周星期天晚上9点左右帖!为了保证JJ的全面性,基本上每天都有当天的JJ在此讨论.
谢谢!

mingja

多谢!

M022girl

***MATH JJ Robert之家 发表于 2003-1-10 0:55:20 D.S. 1. Is the squrae root of N >100? 1) Suare root of (n+1)>100 2) Suare root of (n-1)>100 [确认]B P.S. 2. 一圆内有等腰三角形, 三角形的2边长为10, 求圆面积. [讨论]是等腰么？？是哪两边呢？？感觉不好求 3. There are 20 cars in a dealershop, the cars are of 5 different colors including white cars and red cars. The probablility of picking either a white or red car is less than 3/5. What is the greatest possible number of red cars? [思路]求红车数目的最大可能 已经知道The probablility of picking either a white or red car is less than 3/5 R/20<3/5,W/20<3/5----->R<12,W<12；而且R+W+3OTHER=20 取R为11，可以另令此条件成立=） DS. 4. Line goes through (5,a). Is the slope<0? 1) Line goes through (a,5) 2) Line goes throug (20,a) [思路]代入a=+-1 (5,1)(1,5) (5,-1)(-1,5) ——》slope<0 代入a=5 (5,5)(5,5)——》只有1点，无法判断 (5,a). (20,a) ——》 slope=0 [确认]B 5. What is the value of integer r? a) 4<(r-1)(r-1)<16 b) 4<(r+1)(r-1)<16 [讨论]请大家补充，偶有点看不懂条件 6. What is the variance of 2,3,4,5,6 Given the fomula v=..... [讨论]请大家补充 7. K and P are positive integers. WHich of the followings must have a negative solution? 1. X^2+kX+P=0 2. X^2-kx+p=0 3. 记不起来好像是不对 [思路] X^2+kX+P=0——》 X=+-根号（k^2/2^2-p）-k/2 根号（k^2/2-p）<根号（k^2/2^2）=k/2 所以X都是负的 X^2-kx+p=0——》 X=+-根号（k^2/2^2-p）+k/2 所以X是正的 [确认]A

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littlegal

10． DS :两个同心圆，问两圆面积比？
a) : 两圆周长比=某值
b) : 两圆半径差=某值
Ans : A
显然

Ehy the answer is A?