You’re lucky to have a smart friend, and I think you’re smart as well since you listened to your friend and “asked a Rabbi”. I know about the riddle and it is based on the following true case that occurred in Europe, which deals with division of property, and was resolved with what might appear to be a “surprising” ruling. Here’s the riddle and the correct answer. You can tell your friend the answer and you can even write back sometime and I can share a different riddle with you that you can ask him!
There were two travelers, Reuven and Shimon, who had stopped to eat their meal. Reuven had three portions of food with him, while Shimon had two portions. Before they began to eat, a stranger came by and told them he had no food at all, and asked if they would share their food with him. They agreed. After the meal, the stranger told them that he had five coins with him, which he would give them in payment. Of course, Reuven felt that he was entitled to three of the five coins, since he had contributed three portions, while Shimon had contributed only two. Shimon, on the other hand, argued that they had agreed to share with the stranger, and therefore they should split the five coins equally – two and a half each. They brought the case to the local Rabbi, who ruled that Reuven should get four of the coins, and Shimon should get only one!
The Rabbi’s decision was based on the following reasoning. For ease of calculation, divide each of the five portions into thirds, so altogether, between Reuven and Shimon, there were fifteen thirds in the collective pot. Reuven contributed three portions (nine thirds), and Shimon contributed two portions (six thirds). Since the three men shared the pot, each man actually ate five thirds. Therefore, Reuven ate five thirds, and donated four thirds to the stranger, while Shimon also ate five thirds, but donated only one third to the stranger. So it turns out that Reuven should get four coins, while Shimon should get only one!
I hope this is clear and helpful (the math is actually quite elementary).
