1）if r and s are positive integers, is r/s an integer? 1. every factor of s is also a factor of r. 2. every prime factor of s is also a prime factor of r answer (A) 此题应从何下手啊！？我咋感觉1和2都可以呢？
2) At a dinner party, 5 people are to be seated around a circular table. Two seating arrangements are considered different only when the positions of the people are different relative to each other. What is the total number of different possible seating arrangements for the group? Answer (24)
3) At least 100 students at a certain high school study japanese. If 4 percent of the students at the school who study French also study Japanese, do more students at the school study French than Japanese 1. 16 students at the school study both French and Japanese. 2. 10 percent of the students at the school who study Japanese also study French. Answer (B) 这道题的2中10％和题干中的4％不矛盾嘛？完全不理解！ 请nn帮忙解释一下呗！thx
二题： 不考虑“Two seating arrangements are considered different only when the positions of the people are different relative to each other”的情况下，一共有5！种排法。 如果考虑题中的情况，任意一种排法顺时针（或逆时针）转圈都有5种被视为the same arrangement的排法。所以一共是5!/5=24
1.第一个说S的每一个因素都是R的因素,R的所有因素里面包含了S的所有因素,所以S本身也就是R的一个因素了,所以r/s is an integer. 第二个是说,S的质因素是R的每一个质因素,假设S非质因素的乘积是4*4=16,R的非质因素成绩4*9=36,那r/s就不是整数了,同理可证,另外举例也可以得出r/s是整数.
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发表于 2011-7-4 21:14:53
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