Maths Tips and Tricks from Ziyi

I am not sure if any similar equations out there. But this is really new to me and I never thought before. I will call this is Zi Yi's invention! or Zi Yi's Math Theory. 

This is what he told me.....
ziyi: Mama,  I wish I can write my formula too.....
Me: write la...
X Days... over....
ziyi: mama, I found that we can do this. (1 + 2 )* 3 - 4 / 5 = 1. Interesting right?
Me: Yupe, very interesting. But I think it will be better if you have a equation with 1,2,3,4,5,6 like that.
ziyi: Then 1+2, *3, -4, /5, +6 =7 lo
(((((1+2)*3)-4)/5)+6)=7
Me: Wow... 你之前已经有想过了对吗？
ziyi: No, I just do base on your question.
Me: ziyi, this is call requirements ( 职业病）

ziyi: mama, there are short cut to do multiplication 9, and other numbers. I wonder if I also can come out some short cut or tricks.
In order to count like a clock for multiplication 5 I think we can come out a  formula.
And I finally found one.
Me: Really?
ziyi: Give me a number. Just any number
Me: 250
ziyi: 250 * 5 it will be 250 divided by 2 times 10. So, 250/2 *10 = 125 * 10 = 1250
ziyi: give me another number
Me: 24?
ziyi: still the same, 24 / 2 * 10 = 120
Me: wow....!!!
ziyi: you know why? This is because 10 / 2 = 5!

ziyi: Ehhh... maybe we can try divided by 5. Let's try times 2 divided by 10
ziyi: Give me any number
Me: 250
ziyi: If divided by 5 then the short cut is divided by 2 and times 10. So, 250 * 2 / 10 = 500 / 10 = 50.

ziyi: wow... it works!

conclusion:
multiplication 5, tricks is divided by 2 times 10
division 5, tricks is times 2 divided by 10

Seriously .... ziyi you are too amazing!

He very bz with his number again. I don't know what he will going to do with it.