3 for the price of 2 - a common booksale promotion.

My books were priced, Rm8, Rm8, Rm8, Rm10, Rm15, Rm20 respectively.

I had carefully selected my books because I wanted the Rm10 one to be free.
But the cashier insisted that I pay the Rm10 and am only entitled to get the Rm8 free.
I was surprised, and I explained that it doesn't make sense.
What if I pay them separately?
Paying all the three Rm8 together - which is only Rm16 to get the third one free.
And then, paying the latter group which entitles me to the Rm10 one free. She would still have to do it my way.

The cashier said, "Well, yes... you can... but NO ONE does that."
"Sure they do. I 've worked in Borders before. And they don't even need to do so. The computer auto detects in order for this promotion to be fair to the customers."
Cashier rolled her eyes and just continued with my first transaction.

It was really very UNpleasant.
I just don't get some people sometimes...
It wasn't because of the mere Rm2 save.
I just needed things to make sense... that's all...
too much to ask?