50% off is not the same as buy one, get one free. Let's say each Ebook costs $10. On a "buy one, get one free" deal, I have spent $10. On a 50% off deal, I have

50% off is not the same as buy one, get one free. Let's say each Ebook costs $10. On a "buy one, get one free" deal, I have spent $10. On a 50% off deal, I have spent $5