How can I set this cart rule?

[crota]

Hi,

sorry for my english I'm italian.

I installed prestashop last stable version 1.5.4.0

I'm new to prestashop

 

the site is for selling wines in bottles and in bag in box

 

The bag in box are of this sizes: 5 lt, 10 lt, 20 lt

I create a attribute "bag in box" that can have the value 5 lt or 10 lt or 20 lt

 

I want to set a cart rule that do this:

 

"every 20 lt of wine i will gift 5lt of a wine "X" "

 

For example:

 

customer put in the cart:

 

1 x baginbox lt 20...I will gift 1 x bag in box lt.5 of wine "X"

 

customer put in the cart

 

3 x bag in box lt 20....I will gift 3 bag in box lt 5 of wine "X"

 

customer put in the cart

 

2 x bag in box lt 10

1x bag in box lt 20

5 x bag in box lt 5

 

that means 65 lt of wine?....i will gift 3x bag in box lt 5 of wine "X"

 

 

I cant find a way to set this kind of rule!!!...

 

Can someone help me ?

 

Thanks

 

Andrea