If x and 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. C If n and t are positive integers, what is the greatest prime factor of the product nt ?
(1) The greatest common factor of n and t is 5.
(2) The least common multiple of n and t is 105. B those two questions are so similar, but why one is c and one is b?
Each employee on a certain task force is either a manager or a director. What percent of the employees on the task force are directors?
(1) The average (arithmetic mean) salary of the managers on the task force is $5,000 less than the average salary of all employees on the task force.
(2) The average (arithmetic mean) salary of the directors on the task force is $15,000 greater than the average salary of all employees on the task force. Chow to deal with this one? why answer is C?
Is |x - y | > |x | - |y | ?
(1) y < x
(2) xy < 0 B is this formula |x - y | > |x | - |y | always right?
这个题目,要理解他的意思,绝对值x-y表示在数轴上x与y之间的距离,随便举几个数就可以看出,B充分成立。因为xy<0,说明两个数字一个正一个负,所以必然在0的左边和右边,而绝对值x的意思表示x到0的距离,绝对值y的意思表示y到x的距离,很显然B充分推出题目成立。
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