Consider a product is added to a cart with quantity of N and "Buy X and get y" offer is applied i.e. Buy two get one free.
If n = 3 then I could simply apply a discount rate of 33.33 on each product. But my problem occurs when there are more than 3.
If n = 4 then number of free products would still be 1 and I would have to pay full price for 4th product, but if I apply the above method I would be applying discount on the 4th product as well which should not be the case.
This continues for n = 4,5,6,7,8,9,.....
I need a formula to correctly calculate the price with the scheme applied.
Thank you.
Edit: Edited the question as it was not clear. Sorry.
X would be the number of products that needs to be purchased for the offer to apply and N would be the number of products that are actually in the cart.
The simple answer is if one orders $n$ of the product you get $\lfloor \frac n3 \rfloor$ free and pay for $n-\lfloor \frac n3 \rfloor$