how to teach reduce terms

When my child try  reduce 99/141, bigger number easily cause calculation mistake, she thinks she could not divide by 3. I think it could be very beneficial if she know Divisibility rule.

http://en.wikipedia.org/wiki/Divisibility_rule
You don't need teach all numbers, only prime number less than 20, which is 2, 3, 5, 7, 11, 13, 17, 19
Any idea to make problem easily done?
 

所有跟帖： 

• 是simple form吗？99能看到的除数是3，11，先试呗。我们都是学校老师教的，不知咋教的，好像孩子也没问题。 -princessonthepea- ♀ (0 bytes) () 03/05/2014 postreply 11:38:59

• 回复：how to teach reduce terms -kclskcls- ♀ (162 bytes) () 03/05/2014 postreply 15:22:05