Q13:

What is the value of the integer n?

(1)     n(n + 2) = 15

(2)     (n + 2)ⁿ = 125

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.

他的答案是B, 我选的是D, 为什么A不对啊? 谢谢

这道题好象没有问过,我用GWD7-13, 和7-13 查过, 内容和题号不对应

(1)    n(n + 2) = 15， n 可以取3和-5，3（3+2）=15 ,-5（-5+2）=15， 所以n 的值不能确定。

故：选B.

For  (1)     n(n + 2) = 15

Ans : n²+2n-15 = 0  ==> (n-3)(n+5) =0     ==> n-3 =0  or  n+5 =0  ==> n=3 or n=-5

It means that n could be 3 or n could be -5. 

What is the value for n?   If there is no additional information, it cannot be determined since it can be 3 or -5.

So statement 1) alone is not sufficient.    ---------------------------------(a)  The answer to your question:为什么A不对啊

Based on this fact,

A) and D) are not crrect.

For (2), (n+2)ⁿ = 125

Ans: Starting with the smallest number.

n=0    ==>(0+2)⁰=1

n=1    ==>(1+2)¹=3

n=2    ==>(2+2)²=16

n=3    ==> (3+2)³=5³=5x5x5=125

The only possible value for n is 3. So, it means that Statement (2) alone is sufficient. --------(b)

Based on (a) and (b), the answer is B of course.