大牛注意：“费时易错”机经总结讨论！！

khe01

1.a(n)=a(n-1)-a(n-2), n>=2, a1=-1, a2=1, S(1000)=? (answer: ?) 到底是什么呀？
2。股票市盈率那道题: This year stock price increase by k% from last year. Earning increases by m%.P》R 求Price/Earning ratio increases X%. What is the increase of ratio of increase in price and earnings ….问价格比收益的比例上升百分之几？(100*(K-M)/(100+M)) 能简单说一下思路吗？谢谢。
3。一个出租车公司买入时（lots of five）一次买入5辆，租出时（lots of 3） 问如果买入一辆或租出一辆都算是一次(什么的) 那么去年增长了14 辆车 一共是多少次。  
A 3 B 4 C 5 D 6 E 7
此题的关键是理解lots 的含义 答案 买4此 租2次 共6次 （5*4-3*2= 14）
看不懂。。。。是不是我太笨了？？？[em16]

tongxun

1、3
3、设买了M次，租了N次；则5M-3N=14，求M+N=？M、N为正整数。题目就是这样的。

redpot

would you please explain a little more about the first one?  How to get the answer?  Thanks.

pepsi

第一题我的答案怎么是4？

tongxun

先一项一项的列出来，发现每6循环依次和=0

redpot

The answer of NO.1 is 2 ba?

redpot

???  Would you mind telling me how to get it?

fxxu

斑竹说的对,每六项之和为0,则最后和为a997+a998+a999+a1000
从而S(1000)=a1+a2+a2-a1+(-a1)=2a2-a1=2*1-(-1)=3.

tarzan

The answer should be 3. Because
a(n)  =a(n-1)-a(n-2)
a(n-1)=a(n-2)-a(n-3)
;
;
;
a(3)=a(2)-a(1)
so, all the numbers are added, the answer is s=a(999)-a(1)
and, a(n)=a(n-1)-a(n-2)=a(n-2)-a(n-3)-a(n-2)=-a(n-3)
999/3=333 is one odd integer ,and 999/3=332 the remainder is 3
so a(999)=a(3)
s=a(999)-a(1)=a(3)-a(1)=1+1+1=3