[求助]几道数学题

1.what is the value of the integer n?

1. n(n+2)=15

2. (n+2)^{n₌₁₂₅}

_{^{答案为C，我选的是B。理由是既然题目已经说n是整数，那方程2是只有唯一解的。}}

_{^{难道无法单独解方程2，所以选C？}}

_{^{以后遇到这样的题该如何处理，请大家给予解答，谢谢！}}

_{^{————————————————————————————————————————————}}

2. Which of the following fractions has the greatest value?

A.1/(3²*5²)      B.2/(3²*5²)     C.7/(3³*5²)       D.45/(3³*5³)     E.75/(3⁴*5⁵) 

答案为C，我认为是D

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3. A school administrator will assign each student in a group of n students to one of m classrooms.  If 3 < m < 13 < n, is it possible to assign each of the n students to one of the m classrooms so that each classroom has the same number of students assigned to it?

(1)  It is possible to assign each of 3n students to one of m classrooms so that each classroom has the same number of students assigned to it.

(2)  It is possible to assign each of 13n students to one of m classrooms so that each classroom has the same number of students assigned to it.

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.

C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

D. EACH statement ALONE is sufficient.

E. Statements (1) and (2) TOGETHER are NOT sufficient.

Answer:  B        我认为是E

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还有两道题不明白是什么意思，请大家帮忙解释一下，谢谢！

what percent of the distribution is less than m + d ?

A.  16%

B.  32%

C.  48%

D.  84%

E.  92%

Answer:  D               是概念分布？看不懂题意

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Q3:

If the units digit of the three-digit positive integer k is nonzero, what is the tens digit of k?

(1)   The tens digit of k + 9 is 3.

(2)   The tens digit of k + 4 is 2.

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.

C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

D. EACH statement ALONE is sufficient.

E. Statements (1) and (2) TOGETHER are NOT sufficient.

(1)  It is possible to assign each of 3n students to one of m classrooms so that each classroom has the same number of students assigned to it.

(2)  It is possible to assign each of 13n students to one of m classrooms so that each classroom has the same number of students assigned to it.

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.

C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

D. EACH statement ALONE is sufficient.

E. Statements (1) and (2) TOGETHER are NOT sufficient.

Answer:  B        我认为是E

—————————————————————————————————————————————————————

还有两道题不明白是什么意思，请大家帮忙解释一下，谢谢！

what percent of the distribution is less than m + d ?

A.  16%

B.  32%

C.  48%

D.  84%

E.  92%

Answer:  D               是概念分布？看不懂题意

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Q3:

If the units digit of the three-digit positive integer k is nonzero, what is the tens digit of k?

(1)   The tens digit of k + 9 is 3.

(2)   The tens digit of k + 4 is 2.

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.

C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

D. EACH statement ALONE is sufficient.

E. Statements (1) and (2) TOGETHER are NOT sufficient.

第一题我也觉得B对

第二题明显D比C大，分子35<45的呀，答案错了吧

第三题，就是考整除问题 

条件A 3n/m=整数  不能得出n/m=整数 （m=4 5 6 7 8 9 10 11 12; n>13)

条件B 13n/m=整数  n/m一定为整数   因为13不能被m整除，故n必然能被m整除

选B

第四题 在某一人群中的一种特性的分布关于平均数m对称.如果这种特性中的68%分布在与m的一倍标准差(即d)以内,那么分布在小于m+d以内的特性有多少?其实这道题就是考一个标准正态分布的问题 选D

第五题The tens digit of k + 9 is 3.，应理解为The tens digit of （k + 9） is 3，而不是（The tens digit of k）+9is 3。

由条件（1）可知k+9后个位必然进一，故之前十位应是2。

（2）k+4有可能进位，也有可能没进位，因而无法确定

选A

谢谢dianecarton的指点！

签名出自苏轼的《定风波·莫听穿林打叶声》。词的原文是：

莫听穿林打叶声，何妨吟啸且徐行。

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回首向来萧瑟处，归去，也无风雨也无晴。

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