求教数学jj522

lzkisslife

522.DS：一个数被15除余几？1）除5余4   2）除6 余5。

这个题怎么解呢??有谁知道具体过程吗?

bfeffect

C.

easily u can get, either of the condition alone cannot get the unique result.

(1) ==> N = 5m + 4

(2) ==> N = 6n + 5

(1) & (2) ==> N = 30k + 29 (if you dont know how to get this equation, just ask)

(30k + 29)/15, surely you can get the remainder is 14.

Ironpanda

以下是引用bfeffect在2007-10-24 14:38:00的发言：

C.

easily u can get, either of the condition alone cannot get the unique result.

(1) ==> N = 5m + 4

(2) ==> N = 6n + 5

(1) & (2) ==> N = 30k + 29 (if you dont know how to get this equation, just ask)

(30k + 29)/15, surely you can get the remainder is 14.

If N=5m+1

   N=7n+4

what is the conjunctional formula of 1&2?

N=？？

Ironpanda

Confused

[此贴子已经被作者于2007-10-24 14:49:59编辑过]

lzkisslife

以下是引用大洋彼岸369在2007-10-23 4:20:00的发言：

关于这道题目, DS：一个数被15除余几？1）除5余4   2）除6 余5。可以这样解答:

设这个数为S=Am+B. 根据题目可知: N=5a+4 and N=6b+5, 则我们可以求出通项

S=30A+29.(30是5和6的最小公倍数, B是在当a=5,b=4时, S取最小值29) 所以可知余数为14. 这种题目有时候会是PS, 大家注意方法.

刚找到的 谢谢 我明白了

bfeffect

以下是引用Ironpanda在2007-10-24 14:42:00的发言：

If N=5m+1

   N=7n+4

what is the conjunctional formula of 1&2?

N=？？

N = 35 k + 11

11 is coming from when m = 2 and n = 1.