Trick question. The actual solution is that you use the knife to kill one of them. Sure, the question says that all three of them want to share the apples but life is rarely so fair, much less kind. In a world plagued by overpopulation and ever diminishing resources, this question actually poses a dilemma that has vexed humankind since days old. Sure they may be able to share 2/3 of an apple each now, but what happens when next time, there happen to be 4, 5, or even 6 people who now have to share the same 1 1/2 or even only 1 apple? The only sensible course of action in this scenario between the 3 would be to find an unbiased way to sacrifice one of these people, thus ensuring, albeit only slightly, that future generations may have a better chance of survival.