[原创] 10月数学机井汇总讨论版 更新至668

minnie1016

谢谢！！

dot_deng

373.
        5m < m+5 < 10, m是多少
        ？
 (1) m是奇数
（2）m为正

讨论：C；原公式有，5m<m+5, m<5/4, m+5<10, m<5,条件1不足，条件2，不足，条件并列，则m=1,成立

大家对这道题没有意见吗，我觉得应该选A啊，原因如下：

如果m是整数的话，那么就只有0和1满足条件大于2的数都不满足5m < m+5 < 10，因此如果给定了奇数的话，就只能在整数里面选择，那么就只有1了。所以（1）满足条件。对于（2）说m是整数并不排除是分数的可能，例如1/2,1/5都可以啊，所以（2）不可能！！

请大家讨论！

cpcjustin

奇偶可正可负.满足条件（1）有无数个数!

cpcjustin

549. Is  4< 3m < 6?

1). m<-1

2). m> -2

讨论：A；条件1，成立，条件2不一定

觉得这题应选E.怎么是A呢?明显不对嘛,虚心求教!如当M=-7时,4<-21<6?

553. The sides of a right triangle are x+2, x, and x-2, respectively. What is the area of the triangle?

讨论：；(x+2)^2=X^2+(X-2)^2, x=4

 should be x=8, S=24.

557. If N is a common multiple of 75, 98, and 140, which of the following must be true?

I. N is divisible by 9

II. N is divisible by 49

III. N is greater than 14000

讨论：III

75=3*5*5，98=2*7*7，140=2*2*5*7

N至少为2*2*3*5*5*7*7=14700

should choose (I)&(III)

614. A jar contains 4 black marbles and 6 blue marbles. What is the probability that one blue and one black marble will be picked without replacement?

讨论：C₄¹C₆¹/C₁₀²=2/3

I think it should be: C(4,1)*C(6,1)/<C(10,1)*C(9,1)>=4/15

right? because "will be picked without replacement?

"

open to discuss.

617. J 和A分钱（像话吗？），J’ share VS A’ share is 5:3，if J’ share exceeded 5/9 of the sum money, how much is A’ share. 答案有：A 180$, B 270$, C 360$, D 450$, E 540$，我最后猜了270，应该错了，因为后面出了个类似的题。
                    题有问题

don't understand.

linda816

536.per hour x miles, how long will take  y yards(1mile=1xxx yards)
1)x=y
2)y=10
My answer is C

讨论：C；知道速度、距离就可以算时间

I think the answer should be A.

We needn't know the exact value of x&y, the ratio should be enough.

609. If y=x^n+1, x=?

1). y=1

2). n is odd

讨论：A

I think it should be E. Since n might be -1

[此贴子已经被作者于2006-10-24 5:42:48编辑过]

dot_deng

477.N is a commen multiple of 75, 98,140, which of the following is true?

(i) N can be divided by 9, (ii)N can be divided by 49, (iii) N>14000

讨论：(ii)  N最小是2*2*3*5*5*7*7＝14700
    第三个也对啊！！

xiaomantou80

还有4天就考，现在手忙脚乱的不知道该做什么
看到findjuhl的整理。真是感动死掉了！
没有借口退缩了。
开始研读JJ。希望10月28还没换题库。
再次谢谢整理JJ的XDJM，辛苦啦！！

dot_deng

557. If N is a common multiple of 75, 98, and 140, which of the following must be true?

I. N is divisible by 9

II. N is divisible by 49

III. N is greater than 14000

讨论：III应该是II和III吧！

75=3*5*5，98=2*7*7，140=2*2*5*7

N至少为2*2*3*5*5*7*7=14700

yangxuemei0111

thanks~~

[此贴子已经被作者于2006-10-26 8:19:43编辑过]

c11627

Oh, much improved, thanks a lot.