求助2道prep的DS题

kikoshanshan

159. If n is a positive integer and r is the remainder when (n - 1)(n + 1) is divided by 24, what is the value of r ?

(1) n is not divisible by 2.

(2) n is not divisible by 3.

答案是C

165.    
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.

答案是A

serenashu

第一个题你用举反例的方法做，带几个数字就可以确定了~~
第二题设男老师有X人，女老师有Y人，用条件1有：0.36X+0.5Y=0.42*1400，X+Y=1400，两个方程两个未知数，可解~~

kikoshanshan

第一个题你用举反例的方法做，带几个数字就可以确定了~~
第二题设男老师有X人，女老师有Y人，用条件1有：0.36X+0.5Y=0.42*1400，X+Y=1400，两个方程两个未知数，可解~~

-- by 会员 serenashu (2010/10/24 12:40:49)

恩，懂了，太感谢了