Look for mathematical formula for three checks

[houin]

Hello I duplicated the module checks and I have make a module three checks.

I would like that the customer can use this module following three factors.

 1 : A minimum of purchase for example of 200 euros.

 

 2: That the first one represents for example 20 %.

 

 3: That the remainder is divided by two.

 

Somebody can he help me, I am on 1.5.6.2. Thank you.