两题数学～没有找到可以让我了解的解法 请教大家.谢谢！ 77. 9031-!-item-!-187;#058&006222 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? (A) 5 (B) 10 (C) 24 (D) 32 (E) 120 ------------------------------------------------------------------------------------------------------------------------------------ 【答案】C 【思路】 若为一直线排法 为5！ 但此题目为圆形 五个人排圈圈... ABCDE BCDEA CDEAB DEABC EABCD 都是一样 故排圈圈时就是5!/5=4! ( 除以五是为了消除每次相邻位置改变时都会有重复的情况) -->不懂为何是除以5? 不是减5? 144. If $1,000 is deposited in a certain bank account and remains in the account along with any accumulated interest, the dollar amount of interest, I , earned by the deposit in the first n years is given by the formula I =1000〔(1 + r/100 )^n - 1〕 , where r percent is the annual interest rate paid by the bank. Is the annual interest rate paid by the bank greater than 8 percent? (1) The deposit earns a total of $210 in interest in the first two years. (2) ( 1 + r/100 )^2 > 1.15 -------------------------------------------------------------------------------------------------------------------------------------------------------- 【答案】A 【思路】 (1) 210 = 1000 0.21=1+ + -1 0.21= + 求得166.4….. The deposit earns a total of $210 in interest in the first two years. 是的…….sufficient -->这个我的想法是,interest 有了,不用算出答案也充分.因为不管答案是大於还是小於 8%,都一定有一个唯一解～快速看下一个条件 (2) >1.15 =1+2 + >1.15 =10000+200r+r2>11500 = >11500 =r+100>105(大约值) 所以 r 可能大於也可能小於 8……insufficient --> 请问这个条件有更快的检验方式吗？ 这解法有点花时间 -- Que Pasa --

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