标题: 深夜求助，努力的筒子们在波？ [打印本页] 作者: 麦兜woo 时间: 2010-12-1 00:35 标题: 深夜求助，努力的筒子们在波？ 1.For a finite sequence of nonzero numbers, the number of variations in sign is defined as the number of pairs of consecutive of the sequence for which the product of the two consecutive terms is negative. What is the number of variations in sign for the sequence 1、-3、2、5、-4、-6？
A one B two C three D four E five
答案是C 原谅我连题目都看不懂~~~~(>_<)~~~~
2.The residents of town X participated in a survey to determine the number of hours per week each resident spent watching TV. The distribution of the results of the survey had a mean of 21 hours and a standard deviation of 6 hours. The number of hours that Pat, a resident of town X, watched TV last week between 1 and 2 standard deviation below the mean, which of the following could be the number of hours that Pat watched TV last week? A 30 B 20 C 18 D 12 E 6
答案选D 求解？
3.At least 100 students at a certain high school study Japanese. If 4% of the students at the school who study French also study Japanese, da more students at the school study French than Japanese?
(1) 16 students at the school study both French and J apanese (2) 10% of the students at the school who study Japanese also study French
条件1可以排除，就是不知道条件2怎么可以推出呢？作者: 小手不离 时间: 2010-12-1 00:45
第一题就是说the number of variations in sign被定义为数列中乘积为负数的一对连续数字的个数吧...作者: fanfantastic 时间: 2010-12-1 00:45
第一道题是定义了the number of variations in sign，即相邻两个数如果乘积为负。 1、-3、2、5、-4、-6，1乘-3乘积为负，-3乘2乘积为负，这样一共有3对。 ：）作者: fanfantastic 时间: 2010-12-1 00:49
第二题，平均数为21，标准差为6，Pat上周看电视的时间是在比平均数低1-2个标准差的范围内。 （21-2×6）<=t<=（21-6） t取值在9到15之间，选D作者: fanfantastic 时间: 2010-12-1 00:53
3.At least 100 students at a certain high school study Japanese. If 4% of the students at the school who study French also study Japanese, da more students at the school study French than Japanese?
(1) 16 students at the school study both French and J apanese (2) 10% of the students at the school who study Japanese also study French