有数学题看不懂答案

lingling002

178. 17649-!-item-!-187;#058&011192

Ifthere are more than two numbers in a certain list, is each of the numbers inthe list equal to 0 ?

(1)  The product of any two numbers in the list isequal to 0.

(2)  The sum of any two numbers in the list isequal to 0.

这个答案是A，但是我怎么觉得答案分析错了啊，求指点迷津

If xand y are positive integers, what is the value of xy ?

(1)  The greatest common factor of x and y is 10.

(2)  The least common multiple of x and y is 180.

---------------------------------------------------------------------------这题对于COmmonfactor 和 common multiple的概念不太明确， 对于答案的解释不太理解，有人可以帮忙分析下如解题吗

lingling002

Of the 1,400 college teachers surveyed, 42 percent said that they considered engaging in research an essential goal.  How many of the college teachers surveyed were women?

(1) In the survey, 36 percent of the men and 50 percent of the women said that they considered engaging in research an essential goal.

(2) In the survey, 288 men said that they considered engaging in research an essential goal.
这题感觉答案解释的也不对啊，选A？我怎么觉得是E呢

liubingzhe

178.题的答案应该是B。A的集合中可以有一个数不是零 也可满足任意两数乘积为零

liubingzhe

common factor 是公约数 就是两个数都包含有的约数 比如12和30的公约数是2. common multiple 是公倍数 就是这个数可以被那两个数整除 比如12和30的最小公倍数是1280. 用拐除法比较容易算最大公约和最小公倍