小女明天下午北京二战，求助三道PREP题（其中两道PREP解答宝典里没有解释）

kirnamilk

第一PREP是关于斜率的，
16.1275-!-item-!-187;#058&000656

Lines n and p lie in the xy-plane.Is the slope of line n less than the slope of line p ?



(1)Lines n and p intersect at the point (5,1).



(2)The y-intercept of line n is greater than the y-intercept of line p.

答案是C，我觉得是E呢？ y-intercept 是y轴截距，截距分正负么，弱弱的问？



还有个截距系列的机经：“8DS:问直线L和直线r 是否平行？（1）忘了好像是推不出的（2）L和r的y轴截距都与r的x轴截距相等，我好像选B”


【by 毛毛】

条件二只是说了两条线y轴截距与其中一条的x轴截距相等，那另一条的x轴截距不知道呀，所以不一定重合的，但一定不平行了，所以选B

请问截距分正负么，y轴截距相等是否意味着两条直线在Y轴过同一点啊？



116.11659-!-item-!-187;#058&007807

A certain junior class has 1,000 students and a certain senior class has 800 students.Among these students, there are 60 sibling pairs, each consisting of 1 junior and 1 senior.If 1 student is to be selected at random from each class, what is the probability that the 2 students selected will be a sibling pair?



(A)3/40,000

(B)1/3,600

(C)9/2,000

(D)1/60

(E)1/15



此题prep宝典里无解答，求高人指点，答案是A

175.18356-!-item-!-187;#058&011490

Before being simplified, the instructions for computing income tax in Country R were to add 2 percent of one's annual income to the average (arithmetic mean) of 100 units of Country R's currency and 1 percent of one's annual income.Which of the following represents the simplified formula for computing the income tax, in Country R's currency, for a person in that country whose annual income is I ?


选项我不记得了，有牛牛做过这道题么，貌似是个50+什么…

小女一战完全败在数学，谢过各位牛人了，明天杀鸡完一定请大家喝鸡汤！顺附挺不错的PREP数学解答宝典，貌似来自台湾同胞...

ypl214

第一个答案就是c啊。你画图就知道line n的slope永远小于line p
截距分正负
第二个 分子是60因为有60种可能。 分母是1000*800。junior中的第一个人可以对senior中的800个。junior的第二个人可以对senior中同样800个，以此类推到junior中的第1000个人。不就是1000*800

satsumakiwi

116.

C60 1/C800 1＊C1000 1
全部機率是1000j取一個乘上800S取一個，分子是60sibling取一對出來。這就是解答!!(不會打下標啦!!)

kirnamilk

感谢楼上二位大侠相助！还有这道也一并指点一下啊！实在看不懂....
175.18356-!-item-!-187;#058&011490

Before being simplified, the instructions for computing income tax in Country R were to add 2 percent of one's annual income to the average (arithmetic mean) of 100 units of Country R's currency and 1 percent of one's annual income.Which of the following represents the simplified formula for computing the income tax, in Country R's currency, for a person in that country whose annual income is I ?