Mystery novels have more elastic demand than required textbooks, because mystery novels have close substitutes and are a luxury good, while required textbooks are a necessity with no close substitutes. If the price of mystery novels were to rise, readers could substitute other types of novels, or buy fewer novels altogether. But if the price of required textbooks were to rise, students would have little choice but to pay the higher price. Thus the quantity demanded of required textbooks is less responsive to price than the quantity demanded of mystery novels.
Required textbooks or mystery novels - Mystery novels will have more elastic demand because they are not necessities compared to textbooks. We cannot do away with textbooks as they are necessary to complete a particular subject. As a result textbooks will have a inelastic demand relative to the mystery novels.
Mystery novels will have a more elastic demand because there are many more substitutes – spy novels, science fiction novels, romance novels, western novels – than there are for the one required textbook.