轉載精華區解答如下,不懂的在第(2),請見下文粗體字
125. 13274-!-item-!-187;#058&009989
If @ denotes one of two arithmetic operations, addition or multiplication, and if k is an integer, what is the value of 3 @ k ?
(1) 2 @ k = 3
(2) 1 @ 0 = k
--------------------------------------------------------------------------------------------------------------------------------------------------------
【答案】A
【思路】
題目說K是integer~@是addition or multiplication~
這題可以用A很如意算出K=1
但是題目不是問k=多少
他是問what is the value of 3 @ k
(1) 我們由 ~ (1) 2 @ k = 3 可推論出2乘以一個整數不可能等於3
所以@是addition ~那k就等於1
2@k = 3 Here @ is + and K is 1…..sufficient
(2) 1@0 = k Here @ can be + or ×
(2),在我看來,不管是+或*,代入原式3@K,都可以求出k的值,+號:3@1=4,*號:1*0 =0
原題的要求不就是可以求出K值即可嗎?為何(2)不行呢?