4.1. Mom baked four raisin buns for breakfast for her two sons. $V$ In the first three buns, she put 7, 7, 23 raisins, and some more in the fourth. It turned out that the boys ate an equal number of raisins and did not divide any bun into parts. How many raisins could Mom have put in the fourth bun? List all the options.
Answer: $9,23,37$ (All answers)

Solution. If the boys ate the buns equally, then the fourth bun can only have 23 raisins. If one of them ate three buns, and the other one, then the one who ate one bun ate the one with the most raisins, which is either the one with 23 raisins or the fourth one. In the first case, the fourth bun has $23-7-7=9$ raisins, and in the second case, it has $-23+7+7=37$ raisins.