Cashier : That will be 70 euros.
Silvanalis: 70 euros! Are you sure? This book costs 30 euros and this one 20 euros. The total should be 50!
Cashier : There is no 50 percent discount on the second book.
Silvanalis: How much is it then?
Cashier : It costs 40 euros.
Silvanalis: In that case, I don't want to buy it anymore!