Cashier : That will be 70 euros.
paulopcmp: 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.
paulopcmp: How much is it then?
Cashier : It costs 40 euros.
paulopcmp: In that case, I don't want to buy it anymore!