[求助]还是prep数学DS的一些题不太明白，请教各位NNs了！

yangliu0401

prep数学-DS2：

#197：

The integers m and p are such that 2 < m < p and m is not a factor of p. If r is the remainder when p is divided by m, is r > 1 ?

(1) The greatest common factor of m and p is 2.

 (2) The least common multiple of m and p is 30.

答案是A，我选D--按条件2给出信息：P&M又最小公倍数为30，又根据题干，2 < m < p 且其中一个不是另一个的因子，只有5&6; 3&10, 折两组相除余数=1，否定回答了问题，这样条件2也就充分了啊。

#184：

If k is an integer greater than 1, is k equal to 2的r次方 for some positive integer r ?

(1) k is divisible by 2的6次方.

(2) k is not divisible by any odd integer greater than 1.

答案是B，我选D--不明白为是么条件1不行啊？能被2的6次方整除的书难道不能被2的r次方整除么？

#129：

If t is a positive integer and r is the remainder when t² + 5t + 6 is divided by 7, what is the value of r ?

(1) When t is divided by 7, the remainder is 6.

(2) When t² is divided by 7, the remainder is 1.

答案是A,我选C，这道题不明白

#117：

What is the remainder when the positive integer n is divided by the positive integer k, where k > 1 ?

(1) n = (k + 1)^3

(2) k = 5

答案是A,我选C

#93：

The lifetimes of all the batteries produced by a certain company in a year have a distribution that is symmetric about the mean m. If the distribution has a standard deviation of d, what percent of the distribution is greater than m + d ?

(1) 68 percent of the distribution lies in the interval from m - d to m + d, inclusive.

(2) 16 percent of the distribution is less than m - d.

答案是D,我选C, 这个答案真觉得有些不对啊

#54：

If y is an integer and y = |x | + x, is y = 0 ?

(1) x < 0

(2) y < 1

答案是D,我选A, 条件2怎能充分呢？如果X=1/3不就不成立

SHJDHKBB9

#54： y is an integer

#93：答案是D.

(1)m 为 m - d 和m + d的中点.故m到m + d为68%/2=34%,然后所问为50-34=16%;

(2)m - d到m为50-16=34%,而m 为 m - d 和m + d的中点,因此m到m + d为34%,然后所问为50-34=16%.

所以选D.

SHJDHKBB9

#129：

{t² + 5t + 6}/7={(t+2)(t+3)}/7 而t is divided by 7, the remainder is 6,因此t+2/7余1,t+3/7余2,进而{(t+2)(t+3)}/7为余2.(一个余数乘另一个余数倒数,不确定,求证).

SHJDHKBB9

更正:也可能不被2的r次方整除

SHJDHKBB9

#197：同问? 谢谢.

yangliu0401

以下是引用SHJDHKBB9在2009-1-6 23:10:00的发言：

#54： y is an integer

#93：答案是D.

(1)m 为 m - d 和m + d的中点.故m到m + d为68%/2=34%,然后所问为50-34=16%;

(2)m - d到m为50-16=34%,而m 为 m - d 和m + d的中点,因此m到m + d为34%,然后所问为50-34=16%.

所以选D.

谢谢SHJD啦~再看一遍54题，惭愧死

yangliu0401

以下是引用SHJDHKBB9在2009-1-6 23:22:00的发言：

#129：

{t² + 5t + 6}/7={(t+2)(t+3)}/7 而t is divided by 7, the remainder is 6,因此t+2/7余1,t+3/7余2,进而{(t+2)(t+3)}/7为余2.(一个余数乘另一个余数倒数,不确定,求证).

“一个余数乘另一个余数倒数”？？看不懂呀这是什么定理呢？

[此贴子已经被作者于2009-1-7 1:57:40编辑过]