[求助]一道数据充分性的分析

akrice

烦请达人帮忙解释一下，我已经看不懂Explanation了。谢谢！

题目:

If · represents one of the operations ＋, －, and ×, is k·(l + m) = (k · l) + (k · m) for all numbers k, l and m?

(1) k · l is not equal to l · k for some numbers k

(2) · represents subtraction

答案：D

Explanation: Since k · 1 = 1 · k for both ＋ and × ( i.e., k + 1 = 1+k and k × 1 = 1 × k for all values of k), according to statement (1), · must represent subtraction. Thus, it can be determined whether k - ( l + m ) = ( k - l ) + ( k - m ) holds for all k, l and m. Note, however, that it is not actually necessary to answer this question, only to see that the answer can be determined. thus, statement (1) alone is sufficient. Because statement (2) gives the information directly that · represents subtraction, statement (2) alone is also sufficient. Therefore, EACH statement ALONE is sufficient to answer the question.

hang13

· 代表一个符号，＋, －, and ×都可能，然后你分别代进去试试呗

h5641

因為 k ·1=1 ·k 可帶入 +跟x (如: k+1=1+k and kx1 = 1x k 對所有的k值都有效), 而根據條件(1),  '·' 一定是針對減法(-)而給的條件. 因此, 這可以決定 是否 k - ( l + m ) = ( k - l ) + ( k - m ) 對所有的k,l,m值都有效.

所以(1) 可以決定 '·' 是減法

(2) 說 '·' 是減法, 那也可以直接決定 k·(l + m) = (k · l) + (k · m) 的結果

所以選D

sxxapple

（1）中除法不可以吗？k=1和不等于1，我怎么觉得选B呢？

kykosd

呵呵，是没有仔细看题目的原因吧，，，

题目说If · represents one of the operations ＋, －, and ×, 没有除法这个选项呢