1.7. Is marginal utility always diminishing? Con ider playing cards. If playing cards were purchased one at a time, what would be true about the marginal utility of the 51st playing card compared with the marginal utility of the 52nd playing card? Why do you think it's okay for economists to assume that marginal utility diminishes? How does the concept of marginal utility explain why playing cards are not sold individually, but only as entire 52-card decks?