3-4. In a plane, there are \(n\) cogwheels arranged such that the first wheel is engaged with the second by its teeth, the second with the third, and so on. Finally, the last wheel is engaged with the first. Can the wheels in such a system rotate?
Solution 4. Answer: they can when \(n\) is even, they cannot when \(n\) is odd. See the solution to problem 3 for 7th grade.