16、There are 1200 respondents to a poll, each favoring their preference for candidates A, B, and C. 54% favored A, 48% favored B, and 42% favored C, and there is 30% favored both A and B. Whats the largest possible number of respondents favoring C, but not C B, nor C A.
【答案】12000.28=336
【思路】题目问只选C的最大可能数是多少,要使这个数最大,就要满足所有选C的人,都不会同时选A或者B。即P=1-P=1-=1-=0.28。
17、A plane flied a distance of 800 miles at 360m/h with wind speed. And flied back at 260m/h with wind against it. Whats the average speed of the round-trip?
【答案】约等于302m/h
【思路】将题目理解为单程800m,round-trip 1600m,两个时速中已计入风速的影响,不另行计算。则第一段距离800m,时速360m/h,用时20/9h;第二段距离800m,时速260m/h,用时40/13h。则全程的平均时速=1600/=9360/31,约等于302m/h。
18、To travel trip of 40 miles the speed for the first Y miles was X, and the speed for the remaining 40-y is 1.2X. What average speed?
x = 12m/h
y = 20m/h
【答案】选c
【思路】根据题意,应该为y = 20m。只有将和的条件合在一起,同时知道两段路程的长度分配和每段路程的速度,此题才有确定的解。
19、一群鹅,用来做移民试验,30%是公的,在移民的鹅中20%是公的,问:公鹅的迁徙率比母鹅的迁徙率是多少?
【答案】7/12 分页标题#e#
【思路】设一共有X只鹅,其中30%X是公的,则70%X是母的;设移民的有Y只,其中20%Y是公的,则80%Y是母的,则公的迁移率为0.2Y/0.3X,那么母的迁移率为0.8Y/0.7X
因此公鹅的迁移率比母鹅的迁移率是/=/=7/12
20、r方法和s方法不同,在r方法下的6,24分别对应s方法下的30,60,r和s成linear关系,问:要得到s方法下的100,应该在r方法下是多少?
【答案】48
【思路】因r与s成线性关系,所以r与s的关系可列出方程:s = ar + b,将r=6,24和s=30,60分别带入方程,求得a=5/3,b=20,即s=5/3r+20,再将s=100带入。
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