太浪费时间了，哪位有更好的办法呀！！GWD-4-35

citicsbond

3-35. if n is a positive integer, which of the following is a possible value of |56-5n|?

 - I just simply put every answer to the equation for testing, which i think is quite awkward.....so anybody has a better idea?

silviaqiu

please paste the whole question including the choices.thx

bigtone

就5个选项，都试一下很快的。如果一定要研究的话,可以用n=12做分界，去掉绝对值，

得出 该绝对值的两个等式：

n<12 时，值为 5P+1     10=>p>=0

n>=12时 值为 5k+4  k>=1

不过，我觉得还不一定有代进去快

tsaibh2001

這題我是用了代入數字去找答案 可是怎麼也想不到答案居然會是9咧 請牛人指點

7, 56-5n = 7, 5n=49, n is not an integer

9, 56-5n = 9, 5n=47, n is not an integer

12, 56-5n = 12, 5n=44, n is not an integer

15, 56-5n = 15, 5n=41, n is not an integer

20, 56-5n = 20, 5n=36, n is not an integer

還是說 題目是在問哪一個答案最接近呢...

jh1904

|56-5n|=9, 56-5n=9 or -9, 5n=47 or 65, n=13, 9 is the right answer.

tsaibh2001

喔~~~~~ 原來是這樣喔 難怪要絕對質

受教了 多謝

蔬菜小丸子

我觉得这题 还蛮有价值的 不知道为什么涛涛专门讨论页面没有这题 还好这里有帖子

bubumouse

以下是引用citicsbond在2006/7/21 13:54:00的发言：

3-35. if n is a positive integer, which of the following is a possible value of |56-5n|?

 - I just simply put every answer to the equation for testing, which i think is quite awkward.....so anybody has a better idea?

这样子吧 5的倍数只可能是0或者5结尾 那么56-5n只可能是1或6结尾，5n-6只可能是4或9结尾，所以尾数只能是1，4，6，9  看答案选就可以了

[此贴子已经被作者于2009/8/23 12:01:42编辑过]

babiecrystal

以下是引用bubumouse在2009/8/23 12:00:00的发言：

这样子吧 5的倍数只可能是0或者5结尾 那么56-5n只可能是1或6结尾，5n-6只可能是4或9结尾，所以尾数只能是1，4，6，9  看答案选就可以了

同意~