請問3題數學
If a and b are positive integers such that a-b and a/b are both even
integers, which of the following must be an odd integer?
A. a/2
B. b/2
C. (a+b)/2
D. (a+2)/2
E. (b+2)/2
答案是D 不過我覺得很怪理由如下
題目說a-b & a/b都是偶數
所以我可以得知a & b 都是偶數才對
那D的a+2/2應該也是偶數阿
請問我是哪裡想錯了??
還有2題完全沒頭緒
Is 31 a factor of both x and y?
(1)31^2 is a factor of x and y
(2)31^2 is not a factor of least common multiple of x and y
請問這題 合在一起想 怎麼想才對 答案是C
最後一題
Is positive integer n odd??
(1)n is divisiable by 3
(2)2n is divisiable by twice as many positive integer as n
我知道(1)一定錯
那正解B該怎麼想
麻煩大家 謝謝
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