增求其他數學解法

hijenny · 发表于 2010-6-24 23:45:20

OG 12th Ds 120.
The annual rent collected by a corporation form a certain building was x percent more in 1998 than in 1997 and y percent less in 1999 than in 1998. Was the annual rent collected by the corporation from the building more in 1999 than in 1997?
1. x>y
2. xy/100< x-y

我的解法設rent :R
x/100乘以R +R1997=R1998
R1998- R乘以y/100= R1999
R1998-R乘以y/100> R1998-R乘以x/100
因此1 成立可是答案是B 也就是1 不成立
請教各位大牛我的算法哪裡出錯了??????
感恩!

hijenny · 发表于 2010-7-3 19:45:15

35.3076-!-item-!-187;#058&003114

If p and n are positive integers and p > n, what is the remainder when p² - n² is divided by 15 ?

(1)The remainder when p + n is divided by 5 is 1.

(2)The remainder when p - n is divided by 3 is 1.

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【答案】E

【思路】
=(p+n)(p-n)
(1) p+n=5a+1 ----------------------------------------------------------------------insufficient

(2) p-n=3b+1 -----------------------------------------------------------------------insufficient

(1)(2)(p+n)(p-n)=(5a+1)(3b+1)=15ab+5a+3b+1 ---------------------------insufficient
有哪位戰友能幫我解說這解答??

增求其他數學解法

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