HCF !!!! 18,13

There is no need for calculation for this question.
HCF is the largest common factor among those numbers
As 18 and 13 do not have common factor besides 1,
HCF of 18 and 13 is 1.

If you really want to write calculation,
you may use this.
Breakdown the number into products of prime number.
18=2*3*3
13=13
As 18 and 13 do not have common factor besides 1,
HCF of 18 and 13 is 1.

2013-06-13 23:21:33 補充：
BY comment of ☂雨後晴空☀
要用輾轉相除來列式~

I do not know whether your bother know this.
I remembered it learned in form 6/7.

https://skydrive.live.com/redir?resid=A3980BFF0EA16013!181&authkey=!AJgp4xZXGVduSvE

2013-06-14 07:00:48 補充：
不是吧?
我中一沒教呢..
教輾轉相除時是跟函數一起教

18的因數有:1,2,3,6,9,18
13的因數有:1,13

所以18 和 13 HCF 是 1。

18=1*2*3*3
13=1*13
HCF=大家的common factor, 而家只得1係，所以答案就係1。

要用輾轉相除來列式~

2013-06-13 23:29:00 補充：
我小學時老師都有教,中一也有~

我諗唔到式～～
只知答案係1，冇其他數字啦