4. One of the four squirrels broke the honey jar. Grey claimed that the jar was broken by Blackie. But Blackie claimed that it was Firetail who was to blame. Reddy said that he did not break the jar, and Firetail said that Blackie was lying. Only one of the squirrels told the truth. Who told the truth, and who broke the jar?
Answer. Firetail spoke the truth, Redpaw broke the jar.

Solution. Blackie and Firetail contradict each other. Therefore, one of them is telling the truth. Since only one of them is telling the truth, Gray and Redpaw lied. Therefore, Redpaw broke the jar. Blackie said that Firetail was to blame, so he also lied. That leaves Firetail, who said that Blackie was lying, and this is true.

Comment. Correct solution - 20 points. One case missed - 15 points. Only one case considered, giving the answer - 10 points. Solution started, with some progress - 5 points. Solution started, but progress is insignificant - 1 point. Correct answer given without explanation - 1 point.